LINQ to CSV library

by
Matt Perdeck12. 九月 2011 22:39

Download source and sample code
NuGet package

Contents

Introduction
Requirements
Installation
Quick Start
Write Overloads
Read Overloads
Reading Raw Data Rows
Deferred Reading
CsvFileDescription
CsvColumn Attribute
Error Handling

Introduction

This library makes it easy to use CSV files with LINQ queries. Its features include:

Follows the
most common rules for CSV files. Correctly handles data fields that contain commas and line breaks.
In addition to comma, most delimiting characters can be used, including tab for tab delimited fields.
Can be used with an

IEnumarable

of an anonymous class - which is often returned by a LINQ query.
Supports deferred reading.
Supports processing files with international date and number formats.
Supports different character encodings if you need them.
Recognizes a wide variety of date and number formats when reading files.
Provides fine control of date and number formats when writing files.
Robust error handling, allowing you to quickly find and fix problems in large input files.

Requirements

To compile the library, you need a C# 2008 compiler, such as Visual Studio 2008 or Visual C# 2008 Express Edition.
To run the library code, you need to have the .NET 3.5 framework installed.

Installation

These instructions apply to the download with sources and sample code. The NuGet package installs itself.

Download the zip file with the source code, and unzip in a directory.
Open the Code\LINQtoCSV.sln file in Visual Studio.
You'll find that the sources are organized in a solution, with these elements:

Project LINQtoCSV is the actual library.
Project SampleCode has the sample code shown in this article.
Project TestConsoleApplication is a working console application that exercises most of the features of the library. The code is heavily documented.
The directory TestFiles within the TestConsoleApplication project contains test files - both CSV and tab delimited, and with both US and international (Dutch) dates and numbers.

Compile the solution. This will produce a LINQtoCSV.dll file in the
Code\LINQtoCSV\bin directory. You'll need that file to use the library in your own projects.

Quick Start

Reading from a file

In your project, add a reference to the LINQtoCSV.dll you generated duringInstallation.
The file will be read into an

IEnumerable<T>

, where

T

is a data class that you define. The data records read from the file will be stored in objects of this data class. You could define a data class along these lines:

using LINQtoCSV;
using System;

class Product
{
[CsvColumn(Name = "ProductName", FieldIndex = 1)]
public string Name { get; set; }

[CsvColumn(FieldIndex = 2, OutputFormat = "dd MMM HH:mm:ss")]

public DateTime LaunchDate { get; set; }

[CsvColumn(FieldIndex = 3, CanBeNull = false, OutputFormat = "C")]
public decimal Price { get; set; }

[CsvColumn(FieldIndex = 4)]
public string Country { get; set; }

[CsvColumn(FieldIndex = 5)]
public string Description { get; set; }
}

With this definition, you could read into an

IEnumerable<Product>

.

Although this example only uses properties, the library methods will recognize simple fields as well. Just make sure your fields/properties are public.

The optional

CsvColumn

attribute allows you to specify whether a field/property is required, how it should be written to an output file, etc. Full details are availablehere.

Import the

LINQtoCSV

namespace at the top of the source file where you'll be reading the file:

using LINQtoCSV;

Create a

CsvFileDescription

object, and initialize it with details about the file that you're going to read. It will look like this:

CsvFileDescription inputFileDescription = new CsvFileDescription
{
SeparatorChar = ',',
FirstLineHasColumnNames = true
};

This allows you to specify what character is used to separate data fields (comma, tab, etc.), whether the first record in the file holds column names, and a lot more (full
details).

Create a

CsvContext

object:

CsvContext cc = new CsvContext();

It is this object that exposes the

Read

and

Write

methods you'll use to read and write files.

Read the file into an

IEnumerable<T>

using the

CsvContext

object's

Read

method, like this:

IEnumerable<Product> products =
cc.Read<Product>("products.csv", inputFileDescription);

This reads the file products.csv into the variable

products

, which is of type

IEnumerable<Product>

.

You can now access

products

via a LINQ query, a

foreach

loop, etc.:

var productsByName =
from p in products
orderby p.Name
select new { p.Name, p.LaunchDate, p.Price, p.Description };

// or ...foreach (Product item in products) { .... }

To make it easier to get an overview, here is the code again that reads from a file, but now in one go:

CsvFileDescription inputFileDescription = new CsvFileDescription
{
SeparatorChar = ',',
FirstLineHasColumnNames = true
};

CsvContext cc = new CsvContext();

IEnumerable<Product> products =
cc.Read<Product>("products.csv", inputFileDescription);

// Data is now available via variable products.

var productsByName =
from p in products
orderby p.Name
select new { p.Name, p.LaunchDate, p.Price, p.Description };

// or ...foreach (Product item in products) { .... }

You'll find this same code in the SampleCode project in the
sources.

Writing to a file

This is very similar to
reading a file.

In your project, add a reference to LINQtoCSV.dll.
The

Write

method takes a

IEnumerable<T>

and writes each object of type

T

in the

IEnumerable<T>

as a data record to the file. The definition of your data class could look like this:

using LINQtoCSV;
using System;

class Product
{
[CsvColumn(Name = "ProductName", FieldIndex = 1)]
public string Name { get; set; }

[CsvColumn(FieldIndex = 2, OutputFormat = "dd MMM HH:mm:ss")]
public DateTime LaunchDate { get; set; }

[CsvColumn(FieldIndex = 3, CanBeNull = false, OutputFormat = "C")]
public decimal Price { get; set; }

[CsvColumn(FieldIndex = 4)]
public string Country { get; set; }

[CsvColumn(FieldIndex = 5)]
public string Description { get; set; }
}

The optional
CsvColumn attribute allows you to specify such things as what date and number formats to use when writing each data field. Details for all CsvColumn properties (

CanBeNull

,

OutputFormat

, etc.) are availablehere.

Although this example only uses properties, you can also use simple fields.

The

Write

method will happily use an anonymous type for

T

, so you can write the output of a LINQ query right to a file. In that case, you obviously won't define

T

yourself.Later
on, you'll see an example of this.

Import the

LINQtoCSV

namespace at the top of the source file where you'll be writing the file:

using LINQtoCSV;

Make sure the data is stored in an object that implements

IEnumerable<T>

, such as a

List<T>

, or the

IEnumerable<T>

returned by the

Read

method.

List<Product> products2 = new List<Product>();
// Fill the list with products
// ...

Create aCsvFileDescription object, and initialize it with details about the file you will be writing, along these lines:

CsvFileDescription outputFileDescription = new CsvFileDescription
{
SeparatorChar = '\t', // tab delimited
FirstLineHasColumnNames = false, // no column names in first record
FileCultureName = "nl-NL" // use formats used in The Netherlands
};

Create a

CsvContext

object:

CsvContext cc = new CsvContext();

Invoke the

Write

method exposed by the

CsvContext

object to write the contents of your

IEnumerable<T>

to a file:

cc.Write(
products2,
"products2.csv",
outputFileDescription);

This writes the

Product

objects in the variable

products2

to the file "products2.csv".

Here is the code again that writes a file, but now in one go:

List<Product> products2 = new List<Product>();
// Fill the list with products
// ...
CsvFileDescription outputFileDescription = new CsvFileDescription
{
SeparatorChar = '\t', // tab delimited
FirstLineHasColumnNames = false, // no column names in first record
FileCultureName = "nl-NL" // use formats used in The Netherlands
};

CsvContext cc = new CsvContext();

cc.Write(
products2,
"products2.csv",
outputFileDescription);

Writing an IEnumerable of anonymous type

If you have a LINQ query producing an

IEnumerable

of anonymous type, writing that

IEnumerable

to a file is no problem:

CsvFileDescription outputFileDescription = new CsvFileDescription
{
.....
};

CsvContext cc = new CsvContext();

// LINQ query returning IEnumerable of anonymous type
// into productsNetherlands
var productsNetherlands =
from p in products
where p.Country == "Netherlands"
select new { p.Name, p.LaunchDate, p.Price, p.Description };

// Write contents of productsNetherlands to file
cc.Write(
productsNetherlands,
"products-Netherlands.csv",
outputFileDescription);

Here, a LINQ query selects all products for "Netherlands" from the variable

products

, and returns an

IEnumerable

holding objects of some anonymous type that has the fields

Name

,

LaunchDate

,

Price

, and

Description

. The

Write

method then writes those objects to the fileproducts-Netherlands.csv.

CsvContext.Write Overloads

Write<T>(IEnumerable<T> values, string fileName)

Write<T>(IEnumerable<T> values, string fileName, CsvFileDescription fileDescription)

Write<T>(IEnumerable<T> values, TextWriter stream)

Write<T>(IEnumerable<T> values, TextWriter stream, CsvFileDescription fileDescription)

Some interesting facts about these overloads:

None of the overloads return a value.
Unlike the

Read

method,

Write

does not require that

T

has a parameterless constructor.
Overloads that take a stream write the data to the stream. Those that take a file name write the data to the file.
Overloads that do not take aCsvFileDescription object simply create one themselves, using the default values for the

CsvFileDescription

properties.

CsvContext.Read Overloads

Read<T>(string fileName)

Read<T>(string fileName, CsvFileDescription fileDescription)

Read<T>(StreamReader stream)

Read<T>(StreamReader stream, CsvFileDescription fileDescription)

Some interesting facts about these overloads:

Each overload returns an

IEnumerable<T>

.

T

must have a parameterless constructor. If you do not define a constructor for

T

, the compiler will generate a parameterless constructor for you.
Overloads that take a stream read the data from the stream. Those that take a file name read the data from the file. However, see the section ondeferred
reading.
Overloads that do not take aCsvFileDescription object simply create one themselves, using the default values for the

CsvFileDescription

properties.

Reading Raw Data Rows

Sometimes it's easier to read the raw data fields from the CSV file, instead of having them processed into objects by the library. For example if different rows can have different formats, or if you don't know at compile time which field is going to hold
what data.

You can make this happen by having your type T implement the interface

IDataRow

. This interface is included in the library, so you don't have to write it yourself. It essentially just describes a collection of

DataRowItem

objects:

The

DataRowItem

class is also defined in the library. It describes each individual field within a data row:

public interface IDataRow
{
// Number of data row items in the row.
int Count { get; }

// Clear the collection of data row items.
void Clear();

// Add a data row item to the collection.
void Add(DataRowItem item);

// Allows you to access each data row item with an array index, such as
// row[i]
DataRowItem this[int index] { get; set; }
}

public class DataRowItem
{
...
// Line number of the field
public int LineNbr  { get { ... } }

// Value of the field
public string Value { get { ... } }
}

public class DataRowItem
{
...
// Line number of the field
public int LineNbr  { get { ... } }

// Value of the field
public string Value { get { ... } }
}

The line number is included in the

DataRowItem

class, because data rows can span multiple lines.

The easiest way to create a class that implements

IDataRow

is to derive it from

List<DataRowItem>

:

using LINQtoCSV;

internal class MyDataRow : List<DataRowItem>, IDataRow
{
}

Now you can read the CSV file into a collection of

MyDataRow

objects:

IEnumerable<MyDataRow> products =
cc.Read<MyDataRow>("products.csv", inputFileDescription);

You can then access each individual field within each data row:

foreach (MyDataRow dataRow in products)
{
string firstFieldValue = dataRow[0].Value;
int firstFieldLineNbr = dataRow[0].LineNbr;

string secondFieldValue = dataRow[1].Value;
int secondFieldLineNbr = dataRow[1].LineNbr;

...
}

Deferred Reading

Here is how the

Read

overloads implement deferred reading:

When you invoke the

Read

method (which returns an

IEnumerable<T>

), no data is read yet. If using a file, the file is not yet opened.
When the Enumerator is retrieved from the

IEnumerable<T>

(for example, when starting a

foreach

loop), the file is opened for reading. If using a stream, the stream is rewound (seek to start of the stream).
Each time you retrieve a new object from the Enumerator (for example, while looping through a

foreach

), a new record is read from the file or stream.
When you close the Enumerator (for example, when a

foreach

ends or when you break out of it), the file is closed. If using a stream, the stream is left unchanged.

This means that:

If reading from a file, the file will be open for reading while you're accessing the

IEnumerable<T>

in a

foreach

loop.
The file can be updated in between accesses. You could access the

IEnumerable<T>

in a

foreach

loop, then update the file, then access the

IEnumerable<T>

again in a

foreach

loop to pick up the new data, etc. You only need to call

Read

once at the beginning, to get the

IEnumerable<T>

.

CsvFileDescription

The

Read

and

Write

methods need some details about the file they are reading or writing, such as whether the first record contains column names.

As shown in the
Reading from a file and
Writing to a file examples, you put those details in an object of type

CsvFileDescription

, which you then pass to the

Read

or

Write

method. This prevents lengthy parameter lists, and allows you to use the same details for multiple files.

A

CsvFileDescription

object has these properties:

SeparatorChar
QuoteAllFields
FirstLineHasColumnNames
EnforceCsvColumnAttribute
FileCultureName
TextEncoding
DetectEncodingFromByteOrderMarks
MaximumNbrExceptions

SeparatorChar

Type:	char
Default:	','
Applies to:	Reading and Writing

Example:

CsvFileDescription fd = new CsvFileDescription();
fd.SeparatorChar = '\t'; // use tab delimited file

CsvContext cc = new CsvContext();
cc.Write(data, "file.csv", fd);

The character used to separate fields in the file. This would be a comma for CSV files, or a '\t' for a tab delimited file.

You can use any character you like, except for white space characters or the double quote (").

QuoteAllFields

Type:	bool
Default:	false
Applies to:	Writing only

Example:

fd.QuoteAllFields = true; // forces quotes around all fields

When

false

,

Write

only puts quotes around data fields when needed, to avoid confusion - for example, when the field contains the

SeparatorChar

or a line break.

When

true

,

Write

surrounds all data fields with quotes.

FirstLineHasColumnNames

Type:	bool
Default:	true
Applies to:	Reading and Writing

Example:

fd.FirstLineHasColumnNames = false; // first record does not have column headers

When reading a file, tells

Read

whether to interpret the data fields in the first record in the file as column headers.

When writing a file, tells

Write

whether to write column headers as the first record of the file.

EnforceCsvColumnAttribute

Type:	bool
Default:	false
Applies to:	Reading and Writing

Example:

fd.EnforceCsvColumnAttribute = true; // only use fields with [CsvColumn] attribute

When

true

,

Read

only reads data fields into public fields and properties with the

[CsvColumn]

attribute, ignoring all other fields and properties. And,

Write

only writes the contents of public fields
and properties with the

[CsvColumn]

attribute.

When

false

, all public fields and properties are used.

FileCultureName

Type:	string
Default:	current system setting
Applies to:	Reading and Writing

Example:

fd.FileCultureName = "en-US"; // use US style dates and numbers

Different cultures use different ways to write dates and numbers. 23 May 2008 is 5/23/2008 in the United States (en-US) and 23/5/2008 in Germany (de-DE). Use the

FileCultureName

field to tell

Read

how to interpret the dates and numbers
it reads from the file, and to tell

Write

how to write dates and numbers to the file.

By default, the library uses the current language/country setting on your system. So, if your system uses French-Canadian (fr-CA), the library uses that culture unless you override it with

FileCultureName

.

The library uses the same culture names as the .NET "

CultureInfo

" class (full list of names).

TextEncoding

Type:	Encoding
Default:	Encoding.UTF8
Applies to:	Reading and Writing

Example:

fd.TextEncoding = Encoding.Unicode; // use Unicode character encoding

If the files that you read or write are in English, there is no need to set

TextEncoding

.

However, if you use languages other than English, the way the characters in your files are encoded may be an issue. You will want to make sure that the encoding used by the library matches the encoding used by any other programs (editors, spreadsheets) that
access your files.

Specifically, if you write files with the Euro symbol, you may need to use Unicode encoding, as shown in the example.

DetectEncodingFromByteOrderMarks

Type:	bool
Default:	true
Applies to:	Reading only

Example:

fd.DetectEncodingFromByteOrderMarks = false; // suppress encoding detection

Related to

TextEncoding

. The default normally works fine.

Tells

Read

whether to detect the encoding of the input file by looking at the first three bytes of the file. Otherwise, it uses the encoding given in the

TextEncoding

property.

MaximumNbrExceptions

Type:	int
Default:	100
Applies to:	Reading only

Example:

fd.MaximumNbrExceptions = -1; // always read entire file before throwing AggregatedException

Sets the maximum number of exceptions that will be aggregated into an

AggregatedException

.

To not have any limit and read the entire file no matter how many exceptions you get, set

AggregatedException

to -1.

For details about aggregated exceptions, see the
error handling section.

CsvColumn Attribute

As shown in the
Reading from a file and
Writing to a file examples, you can decorate the public fields and properties of your data class with the

CsvColumn

attribute to specify such things as the output format for date and number fields.

Use of the

CsvColumn

attribute is optional. As long as the
EnforceCsvColumnAttribute property of theCsvFileDescription object you pass into

Read

or

Write

is

false

, those methods will look at all public fields and properties in the data class. They will then simply use the defaults shown with each

CsvColumn

property below.

The

CsvColumn

attribute has these properties:

Name
CanBeNull
NumberStyle
OutputFormat
FieldIndex

Name

Type:	string
Default:	Name of the field or property
Applies to:	Reading and Writing

Example:

[CsvColumn(Name = "StartDate")]
public DateTime LaunchDate { get; set; }

The

Read

and

Write

methods normally assume that the data fields in the file have the same names as the corresponding fields or properties in the class. Use the

Name

property to specify another name for the data field.

CanBeNull

Type:	bool
Default:	true
Applies to:	Reading only

[CsvColumn(CanBeNull = false)]
public DateTime LaunchDate { get; set; }

If

false

, and a record in the input file does not have a value for this field or property, then the

Read

method generates aMissingRequiredFieldException
exception.

FieldIndex

Type:	bool
Default:	Int32.MaxValue
Applies to:	Reading only

Example:

[CsvColumn(FieldIndex = 1)]
public DateTime LaunchDate { get; set; }

This property is used for both reading and writing, but in slightly different ways.

Reading - The

Read

method needs to somehow associate data fields in the input file with field and properties in the data class. If the file has column names in the first record, that's easy -

Read

simply matches
the column names with the names of the fields and properties in the data class.

However, if the file does not have column names in the first record,

Read

needs to look at the order of the data fields in the data records to match them with the fields and properties in the data class. Unfortunately though, the .NET framework
does not provide a way to reliably retrieve that order from the class definition. So, you have to specify which field/property comes before which field/property by giving the fields and properties a

CsvColumn

attribute with the

FieldIndex

property.

The

FieldIndex

s do not have to start at 1. They don't have to be consecutive. The

Read

and

Write

methods will simply assume that a field/property comes before some other field/property if its

FieldIndex

is
lower.

Writing - The

Write

method uses the

FieldIndex

of each field or property to figure out in what order to write the data fields to the output file. Field and properties without

FieldIndex

get written last,
in random order.

NumberStyle

Type:	NumberStyles
Default:	NumberStyles.Any
Applies to:	Reading of numeric fields only

Example:

[CsvColumn(NumberStyle = NumberStyles.HexNumber)]
public DateTime LaunchDate { get; set; }

Allows you to determine what number styles are allowed in the input file (list of options).

By default, all styles are permitted, except for one special case. In order to accept hexadecimal numbers that do not start with 0x, use

NumberStyles.HexNumber

, as shown in the example.

OutputFormat

Type:	string
Default:	"G"
Applies to:	Writing only

Example:

[CsvColumn(OutputFormat = "dd MMM yy")]
public DateTime LaunchDate { get; set; }

Lets you set the output format of numbers and dates/times. The default "G" format works well for both dates and numbers most of the time.

When writing a date/time or number field, the

Write

method first determines the type of the field (

DateTime

,

decimal

,

double

, etc.) and then calls the

ToString

method for that type, with the given

OutputFormat

. So, in the example above, if

LaunchDate

is 23 November 2008, the field written to the file will be "23 Nov 08".

With many formats, the final result depends on the language/country of the file, as set in theFileCultureName property of theCsvFileDescription
object. So, if

LaunchDate

is 23 November 2008 and you specify the short date format:

[CsvColumn(OutputFormat = "d")]
public DateTime LaunchDate { get; set; }

Then, the final value written to the output file will be "11/23/08" if you use US dates (

FileCultureName

is set to "en-US"), but "23/11/08" if you use German dates (

FileCultureName

is set to "de-DE").

Format Codes for DateTime
Standard Numeric Format Strings
Custom Numeric Format Strings

Error Handling

Exception

LINQtoCSVException

BadStreamException
CsvColumnAttributeRequiredException
DuplicateFieldIndexException
RequiredButMissingFieldIndexException
ToBeWrittenButMissingFieldIndexException
NameNotInTypeException
MissingCsvColumnAttributeException
TooManyDataFieldsException
TooManyNonCsvColumnDataFieldsException
MissingFieldIndexException
MissingRequiredFieldException
WrongDataFormatException
AggregatedException

When the

Read

and

Write

methods detect an error situation, they throw an exception with all information you need to solve the problem. As you would expect, all exceptions are derived from the .NET classException.

Retrieving error information

In addition to such properties as

StackTrace

and
Message, the

Exception

class exposes the
Data property. The

Read

and

Write

methods use that property to provide exception information in a way that is easy for your code to read, while they provide error messages targeted at humans via the

Message

property.

The description for each exception (further below) shows what information is stored in the

Data

property.

Aggregating exceptions

When the

Read

method detects an error while reading data from a file, it does not throw an exception right away, but stores it in a list of type

List<Exception>

. Then, after it has processed the file, it throws a single exception
of typeAggregatedException, with the list of exceptions in its

Data["InnerExceptionsList"]

property. This allows you
to fix all problems with an input file in one go, instead of one by one.

You can limit the number of exceptions that get aggregated this way by setting theMaximumNbrExceptions property of theCsvFileDescription
object that you pass to the

Read

method. By default,

MaximumNbrExceptions

is set to 100. When the limit is reached, the

AggregatedException

is thrown right away, with the list of exceptions aggregated so far.

Not all exceptions get aggregated! Before

Read

starts reading data from a file, it first processes column names,

CsvColumn

attributes, etc. If something goes wrong during that preliminary stage, it throws an exception right away.

Deferred reading

Keep in mind that due to
deferred reading, you can get exceptions not only when you invoke the

Read

method, but also when you access the

IEnumerable<T>

that is returned by the

Read

method.

Example

The following code reads a file and processes exceptions. To show how to use the

Data

property, it includes some special processing for the

DuplicateFieldIndexException

- thrown when the

Read

and

Write

methods detect two fields or properties with the sameFieldIndex.

public static void ShowErrorMessage(string errorMessage)
{
// show errorMessage to user
// .....
}

public static void ReadFileWithExceptionHandling()
{
try
{
CsvContext cc = new CsvContext();
CsvFileDescription inputFileDescription = new CsvFileDescription
{
MaximumNbrExceptions = 50
// limit number of aggregated exceptions to 50
};

IEnumerable<Product> products =
cc.Read<Product>("products.csv", inputFileDescription);

// Do data processing
// ...........

}
catch(AggregatedException ae)
{
// Process all exceptions generated while processing the file

List<Exception> innerExceptionsList =
(List<Exception>)ae.Data["InnerExceptionsList"];
foreach (Exception e in innerExceptionsList)
{
ShowErrorMessage(e.Message);
}
}
catch(DuplicateFieldIndexException dfie)
{
// name of the class used with the Read method - in this case "Product"
string typeName = Convert.ToString(dfie.Data["TypeName"]);

// Names of the two fields or properties that have the same FieldIndex
string fieldName = Convert.ToString(dfie.Data["FieldName"]);
string fieldName2 = Convert.ToString(dfie.Data["FieldName2"]);

// Actual FieldIndex that the two fields have in common
int commonFieldIndex = Convert.ToInt32(dfie.Data["Index"]);

// Do some processing with this information
// .........

// Inform user of error situation
ShowErrorMessage(dfie.Message);
}
catch(Exception e)
{
ShowErrorMessage(e.Message);
}
}

BadStreamException

This exception exposes the same properties as
Exception.

Thrown when a stream is passed to

Read

, which is either

null

, or does not support

Seek

. The stream has to support

Seek

, otherwise it cannot be rewound when the

IEnumarable

returned by

Read

is accessed.

CsvColumnAttributeRequiredException

This exception exposes the same properties as
Exception.

Thrown when the

CsvFileDescription

object that has been passed to

Read

has bothFirstLineHasColumnNames
and
EnforceCsvColumnAttribute set to

false

.

If there are no column names in the file, then

Read

relies on the

FieldIndex

of each field or property in the data class to match them with the data fields in the file. However, if

EnforceCsvColumnAttribute

is

false

,
that implies that fields or properties without the

CsvColumn

attribute can also be used to accept data, while they do not have a

FieldIndex

.

DuplicateFieldIndexException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the class with the offending fields/properties
Data["FieldName"]	string	Fields or properties with a duplicate FieldIndex
Data["FieldName2"]
Data["Index"]	int	Common FieldIndex

Thrown when two or more fields or properties have the same
FieldIndex.

RequiredButMissingFieldIndexException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the class with the offending field/property
Data["FieldName"]	string	Field or property without FieldIndex

When there are no column names in the first record in the file (FirstLineHasColumnNames is

false

),
each required field (CanBeNull attribute set to

false

) must have aFieldIndex
attribute, otherwise it cannot be read from the file.

ToBeWrittenButMissingFieldIndexException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the class with the offending field/property
Data["FieldName"]	string	Field or property without FieldIndex

When writing a file without column names in the first record, you will want to make sure that the data fields appear in each line in a well defined order. If that order were random, it would be impossible for some other program to reliably process the file.

So, when the

Write

method is given aCsvFileDescription with
FirstLineHasColumnNames as

false

, and it finds a field or property that doesn't have a

FieldIndex

, it throws a

ToBeWrittenButMissingFieldIndexException

.

NameNotInTypeException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the class missing the field/property
Data["FieldName"]	string	Field or property that isn't found
Data["FileName"]	string	Name of the input file

If the

Read

method is given aCsvFileDescription with
FirstLineHasColumnNames as

true

, and one of the column names in the first record in the file does not match a field or property, it throws a

NameNotInTypeException

.

MissingCsvColumnAttributeException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the class with the offending field/property
Data["FieldName"]	string	Field or property without CsvColumn attribute
Data["FileName"]	string	Name of the input file

The

Read

method may throw this exception when it is given aCsvFileDescription with both
FirstLineHasColumnNames and
EnforceCsvColumnAttribute as

true

. When

Read

reads the column names from the first record, one of those column names may match a field or property that doesn't have a

CsvColumn

attribute, even though only
fields and properties with a

CsvColumn

attribute can be used. When that happens,

Read

throws a

MissingCsvColumnAttributeException

.

TooManyDataFieldsException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the data class
Data["LineNbr"]	int	Line in the input file with an excess data field
Data["FileName"]	string	Name of the input file

Thrown when a record in the input file has more data fields than there are public fields and properties in the data class.

TooManyNonCsvColumnDataFieldsException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the data class
Data["LineNbr"]	int	Line in the input file with an excess data field
Data["FileName"]	string	Name of the input file

When only fields or properties that have a

CsvColumn

attribute are used (

Read

is given aCsvFileDescription
with
EnforceCsvColumnAttribute as

true

), and a record in the input file has more data fields than there are fields and properties with the

CsvColumn

attribute, a

TooManyNonCsvColumnDataFieldsException

is thrown.

MissingFieldIndexException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the data class
Data["LineNbr"]	int	Line with offending field
Data["FileName"]	string	Name of the input file

If there are no column names in the first record of the input file (

Read

is given aCsvFileDescription withFirstLineHasColumnNames
as

false

), then

Read

relies on theFieldIndex of the fields and properties in the data class to match
them with the data fields in the file.

When a record in the input file has more data fields than there are fields and properties in the data class with a

FieldIndex

, then a

MissingFieldIndexException

is thrown.

MissingRequiredFieldException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the class with the required field/property
Data["FieldName"]	string	Name of the required field/property
Data["LineNbr"]	int	Line where missing field should have been
Data["FileName"]	string	Name of the input file

Thrown when a record from the input file does not have a value for a required field or property (CanBeNull property of theCsvColumn
attribute set to

false

).

Difference between null and empty string

Empty strings and strings consisting of only white space need to be surrounded by quotes, so they are recognized as something other than

null

.

These input lines both have the data fields "abc", null, and "def":

abc,,def
abc,   ,def

While this line has the data fields "abc", followed by the empty string, followed by "def":

abc,"",def

and this line has the data fields "abc", followed by a string with three spaces, followed by "def":

abc,"   ",def

WrongDataFormatException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the class with the field/property
Data["FieldName"]	string	Name of the field/property
Data["FieldValue"]	string	The offending data value
Data["LineNbr"]	int	Line with offending data value
Data["FileName"]	string	Name of the input file

Thrown when a field has the wrong format. For example, a numeric field with the value "abc".

AggregatedException

Additional Properties - This exception exposes the same properties asException, plus these additional properties:

Property	Type	Description
Data["TypeName"]	string	Name of the data class used by Read
Data["FileName"]	string	Name of the input file
Data["InnerExceptionsList"]	List<Exception>	List of Exception s

Used to aggregate exceptions generated while reading a file (more details).

转自：http://www.aspnetperformance.com/post/LINQ-to-CSV-library.aspx