自定义数据类型的数据库映射方案

基础数据类型，如String、Integer、Date、Boolean等它们可以很方便的映射到数据库：

import grails.persistence.Entity

@Entity
class MyEntity {
String code
String name
static constraints = {
code(unique: true, minSize: 4, maxSize: 4)
name(blank: false, maxSize: 255)
}
}

这些基础数据类型是JAVA提供的语言级的，它没有语意。

比如要表达一个身份证号码：它有长度限制：15位或18位；还有规则限制；还能从身份证号码中提取出地址、性别、出生日期、年龄等信息。这些信息用一个String是无法表达，需要用类来描述：

class IDNumber{
String idNumber

Address address
InsDate birthday
Gender gender
IDNumber() {}
IDNumber(val) {
if (val.length() == 15) {
val = to18IdNumber(val)
}
if (val.length() != 18) {
throw new IllegalArgumentException("不是身份证格式")
}
this.idNumber = val
return
}
def getAddress() {
if (address) return address
else return address = parseAddress()
}
def getBirthday() {
if (birthday) return birthday
else return birthday = parseBirth()
}
def getGender() {
if (gender) return gender
else return gender = parseGender()
}
def parseBirth() {
...
}
}

这个类里面最核心的就是String idNumber身份证号码，其他属性都是暂存的临时数据，可以从身份证号码里解析出来。如果想把这个类映射到数据库中，现在只能映射成一个table，但映射成table又不合理，最好是能映射成一列：

@grails.persistence.Entity
class PersonInfo {
String name
IDNumber idNumber
}

现在这样显然是不能达到这个目标的。

Hibernate提供了多种实现自定义类型的方法：

1、实现org.hibernate.usertype.UserType

2、实现org.hibernate.usertype.CompositeUserType

3、实现org.hibernate.usertype.UserCollectionType

4、实现org.hibernate.usertype.EnhanceUserType

通过实现这些接口，可以将自定义数据类型映射成数据库列。

UserType可以映射成单列，CompositeUserType可以映射成多列。

看个例子：

class MyString extends InsDataType implements UserType{
String value

@Override
void buildData(val) {
if (val instanceof MyString) {
value = val.value
return
}
if (val == null) value = null
else if (val instanceof String) value = val
else if (val instanceof Number) value = String.valueOf(val)
else value = val.toString()
return
}

static MyString from(val) {
if (val instanceof MyString) return val
MyString data = new MyString()
data.build(val)
return data
}

public String toString() {
return value
}

int[] sqlTypes() {
return [Types.VARCHAR]
}

Class returnedClass() {
return MyString
}

boolean equals(Object x, Object y) {
MyString mx, my
if (x instanceof String) mx = MyString.from(x)
if (x instanceof MyString) mx = x

if (y instanceof String) my = MyString.from(y)
if (y instanceof MyString) my = y
if (mx?.value == my?.value) return true
return false
}

int hashCode(Object x) {
return ((MyString) x)?.value?.hashCode()
}

Object nullSafeGet(ResultSet rs, String[] names, Object owner) {
if (rs.wasNull()) return null
//        String stringFromDb = (String) Hibernate.STRING.nullSafeGet(rs, names[0]);
String stringFromDb = rs.getString(names[0]);
return MyString.from(stringFromDb)
}

void nullSafeSet(PreparedStatement st, Object value, int index) {
if (value == null)
st.setNull(index, Types.VARCHAR);
else {
MyString myString = (MyString) value;
st.setString(index, myString.value);
//            Hibernate.STRING.nullSafeSet(st, myString.value, index);
}
}

Object deepCopy(Object value) {
if (!value || !((MyString) value).value) return null
return MyString.from(value)
}

boolean isMutable() {
return true
}

Serializable disassemble(Object value) {
return ((MyString) value).value
}

Object assemble(Serializable cached, Object owner) {
return MyString.from(cached)
}

Object replace(Object original, Object target, Object owner) {
return null
}
}

这样就可以将MyString映射到数据库表中的一列了。

@grails.persistence.Entity
class MyEntity {
MyString name
static constraints = {
name(nullable: true)
}
static mapping = {
name(length: 10)
}
}

数据库结构:





测试保存：

def testSave() {
MyEntity entity = new MyEntity(name: MyString.from("hehe"))
TestDomain.withTransaction {
if (entity.hasErrors() || !entity.save(flush: true)) {
println "save error:" + entity.errors
}
}
}

数据库记录为：





测试查询：

MyEntity entity = MyEntity.findByName(MyString.from("hehe"))

现在操作自定义的MyString就像操作基础数据类型一样了。

如果一个数据类型有多个字段要存储，比如姓名分姓氏和名称。一种方法是把多个字段合并成一个字段，仍然使用UserType。另一种方法是用CompositeUserType。

class MyChineseName implements CompositeUserType {
String familyName
String givenName

String[] getPropertyNames() {
return ["familyName", "givenName"] as String[]
}
Type[] getPropertyTypes() {
return [Hibernate.STRING, Hibernate.STRING] as Type[]
}
Object getPropertyValue(Object component, int property) {
MyChineseName name = (MyChineseName) component;
String result;
switch (property) {
case 0:
result = name.familyName;
break;
case 1:
result = name.givenName;
break;
default:
throw new IllegalArgumentException("unknow property: " + property);
}
return result;
}
void setPropertyValue(Object component, int property, Object value) {
MyChineseName name = (MyChineseName) component;
String nameValue = (String) value;
switch (property) {
case 0:
name.familyName = nameValue
break;
case 1:
name.givenName = nameValue
break;
default:
throw new IllegalArgumentException("unknow property: " + property);
}
}
Class returnedClass() {
return MyChineseName
}
boolean equals(Object x, Object y) {
if (x == y)
return true;
if (x == null || y == null)
return false;
return x.equals(y);
}
int hashCode(Object x) {
return x.hashCode()
}
Object nullSafeGet(ResultSet rs, String[] names, SessionImplementor session, Object owner) {
if (rs.wasNull())
return null;
String firstname = rs.getString(names[0]);
String lastname = rs.getString(names[1]);
return new MyChineseName(familyName: firstname, givenName: lastname);
}
void nullSafeSet(PreparedStatement statement, Object value, int index, SessionImplementor session) {
if (value == null)
statement.setNull(index, Types.VARCHAR);
else {
MyChineseName name = (MyChineseName) value;
//            statement.setString(index, name.familyName);
//            statement.setString(index + 1, name.givenName);
Hibernate.STRING.nullSafeSet(statement, name.familyName, index + 0);
Hibernate.STRING.nullSafeSet(statement, name.givenName, index + 1);
}
}
Object deepCopy(Object value) {
if (value == null)
return null;
MyChineseName name = (MyChineseName) value;
return new MyChineseName(familyName: name.familyName, givenName: name.givenName);
}
boolean isMutable() {
return false
}
Serializable disassemble(Object value, SessionImplementor session) {
return (Serializable) deepCopy(value);
}
Object assemble(Serializable cached, SessionImplementor session, Object owner) {
return (Serializable) deepCopy(cached);
}
Object replace(Object original, Object target, SessionImplementor session, Object owner) {
return null
}
}

这样，MyChineseName就能够映射成两列了。如果还像上面一样定义Entity类，Hibernate仍然无法映射，必须指定type和column：

@grails.persistence.Entity
class MyEntity {
MyChineseName name
static constraints = {
name(nullable: true)
}
static mapping = {
name type: MyChineseName, {
column name: "chineseFamilyName", length: 10
column name: "chineseGivenName", length: 10
}
}
}

生成的数据库表结构：





测试保存：

def testSave() {
MyEntity entity = new MyEntity(name: new MyChineseName(familyName: "泛", givenName: "华"))
TestDomain.withTransaction {
if (entity.hasErrors() || !entity.save(flush: true)) {
println "save error:" + entity.errors
}
}
println ToStringBuilder.reflectionToString(entity)
}

数据库记录为：





这种方式的麻烦之处在于映射时需要指定type和column。如果用户不清楚它的实现方式，仍然当作普通的UserType，没有指定type和column，那么就会报错：

Caused by: org.hibernate.MappingException: property mapping has wrong number of columns: com.baoxian.domain.MyEntity.name type: com.baoxian.datatype.MyChineseName

仅仅根据这个错误描述就不太好定位了。

可以把多字段组合成一个字符串，从而映射成一个字段来解决：

class MyChineseName implements UserType {
String familyName
String givenName

String toOneString() {
return "fn:${familyName};gn:${givenName}"
}
MyChineseName parseString(String str) {
def regular = /(fn|gn):([^;]*)/
def result = str =~ regular
def map = [:]
result.each { map[it[1]] = it[2] }
return new MyChineseName(familyName: map["fn"], givenName: map["gn"])
}
int[] sqlTypes() {
return [Types.VARCHAR]
}
Class returnedClass() {
return MyChineseName
}
boolean equals(Object x, Object y) {
if (x == y)
return true;
if (x == null || y == null)
return false;
return x.equals(y);
}
int hashCode(Object x) {
return x.hashCode()
}
Object nullSafeGet(ResultSet rs, String[] names, Object owner) {
return parseString(rs.getString(names[0]))
}
void nullSafeSet(PreparedStatement st, Object value, int index) {
if (value == null)
st.setNull(index, Types.VARCHAR);
else {
MyChineseName name = (MyChineseName) value
st.setString(index, name.toOneString())
}
}
Object deepCopy(Object value) {
if (value == null)
return null;
MyChineseName name = (MyChineseName) value;
return new MyChineseName(familyName: name.familyName, givenName: name.givenName);
}
boolean isMutable() {
return false
}
Serializable disassemble(Object value) {
return (Serializable) deepCopy(value);
}
Object assemble(Serializable cached, Object owner) {
return (Serializable) deepCopy(cached);
}
Object replace(Object original, Object target, Object owner) {
return null
}
}

生成的数据库记录为：





除了实现CompositeUserType能将一个对象映射成多列，还有一种方法能达到这种效果：embedded。它能将本应映射成两个table的组合成一个表。

假设有两个实体关联如下：

@grails.persistence.Entity
class MyComp {
String name
String code
}
@grails.persistence.Entity
class MyEntity {
String keyName
MyComp comp

static constraints = {
comp(nullable: true)
}
}

这样，它会在数据库中映射成两个表，用ID关联起来。





因为关联表很简单，能不能组合成一张表呢？可以，用embedded：

class MyComp {
String name
String code
}
@grails.persistence.Entity
class MyEntity {
String keyName
MyComp comp

static embedded = ['comp']
static constraints = {
comp(nullable: true)
}
}

生成的表为：