使用Asp.Net Core MVC 开发项目实践[第三篇:基于EF Core的扩展]

上篇我们说到了EFCore的基础使用,这篇我们将讲解下基于EFCore的扩展.

我们在Mango.Framework.EFCore类库项目中创建一个类名EFExtended的扩展类,并且引入相关的命名空间

using System;
using System.Reflection;
using System.Collections.Generic;
using System.Data;
using System.Data.Common;
using System.Data.SqlClient;
using Microsoft.EntityFrameworkCore;
using System.Linq;
using System.Linq.Expressions;
namespace Mango.Framework.EFCore
{
public static class EFExtended
{}
}

第一个扩展:基于传统DataTable(这个在2.0中才开始有)的返回

#region 查询返回DataTable的扩展

//自定义SQL语句     
        public static DataTable QueryDataTable(this DbContext context, string sql, params SqlParameter[] parameters)
{
DbConnection connection = null;
DbCommand command = null;
try
{
connection = context.Database.GetDbConnection();
if (connection.State == ConnectionState.Closed)
{
connection.Open();
}
command = connection.CreateCommand();
command.CommandText = sql;
command.Parameters.AddRange(parameters);
DbDataReader reader = command.ExecuteReader();
var result= FillDataTable(reader);
//释放连接资源
command.Dispose();
connection.Close();
//
return result;
}
catch (Exception ex)
{
throw ex;
}
finally
{
//释放连接资源
if (command != null)
{
command.Dispose();
}
if (connection != null)
{
connection.Close();
}
}
}
private static DataTable FillDataTable(DbDataReader reader)
{
bool defined = false;

DataTable table = new DataTable();

while (reader.Read())
{
object[] values = new object[reader.FieldCount];
//插入列信息
if (!defined)
{
for (int i = 0; i < reader.FieldCount; i++)
{
DataColumn column = new DataColumn()
{
ColumnName = reader.GetName(i),
DataType = reader.GetFieldType(i)
};

table.Columns.Add(column);
}

defined = true;
}

//插入数据
reader.GetValues(values);
DataRow dataRow = table.NewRow();
for (int i = 0; i < values.Length; i++)
{
dataRow[i] = values[i];
}
table.Rows.Add(dataRow);
}
return table;
}
#endregion

就是通过DbCommand类执行SQL语句返回DbDataReader的数据集合,将返回的数据集合填充到DataTable实例中去.

第二个扩展:基于SQL语句的查询返回指定的集合对象

using System;
using System.Collections.Generic;
using System.Reflection;
using System.ComponentModel;
namespace Mango.Framework.EFCore
{
public class DbIdentity
{
internal static object Change(object value, Type type)
{
if (type.IsGenericParameter)
{
if (type.IsGenericParameter && type.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
{
if (value == null)
{
return null;
}
NullableConverter nullableConverter = new NullableConverter(type);
value = Convert.ChangeType(value, type);
}
}
return value;
}
}

}