KeyGenerator
KeyGenerator 是用来获取 insert、update 语句 获取数据库主键 id 的。
insert 语句并不会返回自动生成的主键，而是返回插入记录的条数。如果业务
逻辑需要获取插入记录时产生的自增主键，则可以使用 Mybatis 提供的 KeyGenerator 接口。
不同的数据库产品对应的主键生成策略不一样，例如， Oracle 、DB2 等数据库产品是通过 sequence 实现自增 id 的，在执行 insert 语句之前必须明确指定主键的值。
而 MySQL, Postgresql 等数据库在执行 insert 吾句时，可以不指定主键，在插入过程中由数据库自动生成自增主键。、
KeyGenerator 接口针对这些不同的数据库产品提供了对应的处理方法。
public interface KeyGenerator {
// 在执行 insert 之前执行，设置属性 order = "BEFORE"
void processBefore(Executor executor, MappedStatement ms, Statement stmt, Object parameter);
// 在执行 insert 之后执行，设置属性 order = "After"
void processAfter(Executor executor, MappedStatement ms, Statement stmt, Object parameter);
}
UML 类图
image.png
NoKeyGenerator
NoKeyGenerator 虽然实现了 KeyGenerator 接口，但是其中的 processBefore() 方法和 processAfter() 方法都是空实现。
public class NoKeyGenerator implements KeyGenerator {
/**
* A shared instance.
* @since 3.4.3
*/
public static final NoKeyGenerator INSTANCE = new NoKeyGenerator();
@Override
public void processBefore(Executor executor, MappedStatement ms, Statement stmt, Object parameter) {
// Do Nothing
}
@Override
public void processAfter(Executor executor, MappedStatement ms, Statement stmt, Object parameter) {
// Do Nothing
}
}
Jdbc3KeyGenerator
Jdbc3KeyGenerator 用于取回数据库 生成的自增 id,对应 mybatis-config.xml 配置文件中的 useGeneratedKeys 全局配置，以及 insert 节点中 useGeneratedKeys 属性。
mapper 配置
<insert id="test_insert" useGeneratedKeys="true" keyProperty＝”id”〉
INSERT INTO t_user(username , pwd) VALUES
<foreach item= "item" collection=” list” separator=”,”>
(#(item.username}, #(item.pwd})
</foreach>
</insert>
被调用的地方
XMLStatementBuilder 主要用来解析 mapper.xml 中的 insert 、update、delete、select 节点。
XMLStatementBuilder.parseStatementNode() 方法，用来解析 mapper.xml 文件中的节点。其中 insert 节点中配置了获取 主键 Id 的 useGeneratedKeys 的方式。
// Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
KeyGenerator keyGenerator;
// 获取 <selectKey> 节点对应的 SelectKeyGenerator 的 Id
String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
//检测 SQL 节点中 是否 配置了 <selectKey> 节点、SQL 节点的 useGeneratedKeys 属性值；
// <insert> <update> 节点中的 <selectKey> 节点指定了获取数据库主键的方式；
if (configuration.hasKeyGenerator(keyStatementId)) {
keyGenerator = configuration.getKeyGenerator(keyStatementId);
} else {
// 根据 SQL 节点的 useGeneratedKeys 属性值、mybatis-config.xml 中全局的 useGeneratedKeys 配置，以及是否是 insert 语句，决定使用 keyGenerator 的具体接口实现
keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
}
详解 Jdbc3KeyGenerator
Jdbc3KeyGenerator.processBefore() 方法是空实现，只实现了 processAfter() 方法，该方法会调
Jdbc3 KeyGenerator. processBatch() 方法将 SQL 语句执行后生成的主键记录到用户传递的实参中。
在 PreparedStatement 执行完 update 之后，将 SQL 语句执行后生成的主键记录到用户传递的时参数中。一般情况下，对应单行插入操作，传入的实参是一个 JavaBean 对象 或是 Map 对象，则将对象对应一次插入操作的内容；对于多行插入， 传入的实参可以是对象或 Map 对象的数组或集合，集合每一个元素都对应一次插操作。
public class Jdbc3KeyGenerator implements KeyGenerator {
/**
* A shared instance.
*
* @since 3.4.3
*/
public static final Jdbc3KeyGenerator INSTANCE = new Jdbc3KeyGenerator();
private static final String MSG_TOO_MANY_KEYS = "Too many keys are generated. There are only %d target objects. "
+ "You either specified a wrong 'keyProperty' or encountered a driver bug like #1523.";
@Override
public void processBefore(Executor executor, MappedStatement ms, Statement stmt, Object parameter) {
// do nothing
}
@Override
public void processAfter(Executor executor, MappedStatement ms, Statement stmt, Object parameter) {
processBatch(ms, stmt, parameter);
}
/**
* 在 PreparedStatement 执行完 update 之后，将 SQL 语句执行后生成的主键记录到用户传递的时参数中。
* 一般情况下，对应单行插入操作，传入的实参是一个 JavaBean 对象 或是 Map 对象，则将对象对应一次插入操作的内容；
* 对于多行插入， 传入的实参可以是对象或 Map 对象的数组或集合，集合每一个元素都对应一次插操作。
* @param ms
* @param stmt
* @param parameter
*/
public void processBatch(MappedStatement ms, Statement stmt, Object parameter) {
final String[] keyProperties = ms.getKeyProperties();
if (keyProperties == null || keyProperties.length == 0) {
return;
}
try (ResultSet rs = stmt.getGeneratedKeys()) {
final ResultSetMetaData rsmd = rs.getMetaData();
final Configuration configuration = ms.getConfiguration();
if (rsmd.getColumnCount() < keyProperties.length) {
// Error?
} else {
assignKeys(configuration, rs, rsmd, keyProperties, parameter);
}
} catch (Exception e) {
throw new ExecutorException("Error getting generated key or setting result to parameter object. Cause: " + e, e);
}
}
/**
* 处理不同类型 结果实参；Map 类型、ArrayList 类型 等等
* @param configuration
* @param rs sql 执行结果集合
* @param rsmd ResultSet 结果集合的每列的元属性，
* @param keyProperties 指定的自增主键 Id 对应 Java 对象属性
* @param parameter sql 数据库执行之后，数据库传回的参数
* @throws SQLException
*/
@SuppressWarnings("unchecked")
private void assignKeys(Configuration configuration, ResultSet rs, ResultSetMetaData rsmd, String[] keyProperties,
Object parameter) throws SQLException {
if (parameter instanceof ParamMap || parameter instanceof StrictMap) {
// Multi-param or single param with @Param
assignKeysToParamMap(configuration, rs, rsmd, keyProperties, (Map<String, ?>) parameter);
} else if (parameter instanceof ArrayList && !((ArrayList<?>) parameter).isEmpty()
&& ((ArrayList<?>) parameter).get(0) instanceof ParamMap) {
// Multi-param or single param with @Param in batch operation
assignKeysToParamMapList(configuration, rs, rsmd, keyProperties, ((ArrayList<ParamMap<?>>) parameter));
} else {
// Single param without @Param
assignKeysToParam(configuration, rs, rsmd, keyProperties, parameter);
}
}
/**
* 处理 Java 对象或者 Bean 对象，非集合对象，单条数据情况
* @param configuration
* @param rs
* @param rsmd
* @param keyProperties
* @param parameter
* @throws SQLException
*/
private void assignKeysToParam(Configuration configuration, ResultSet rs, ResultSetMetaData rsmd,
String[] keyProperties, Object parameter) throws SQLException {
Collection<?> params = collectionize(parameter);
if (params.isEmpty()) {
return;
}
List<KeyAssigner> assignerList = new ArrayList<>();
for (int i = 0; i < keyProperties.length; i++) {
assignerList.add(new KeyAssigner(configuration, rsmd, i + 1, null, keyProperties[i]));
}
Iterator<?> iterator = params.iterator();
while (rs.next()) {
if (!iterator.hasNext()) {
throw new ExecutorException(String.format(MSG_TOO_MANY_KEYS, params.size()));
}
Object param = iterator.next();
assignerList.forEach(x -> x.assign(rs, param));
}
}
/**
* 处理 List 类型，遍历数据库生成的主键结果集，并设置到 Parameters 集合对应的元素的属性中
* @param configuration
* @param rs
* @param rsmd
* @param keyProperties
* @param paramMapList
* @throws SQLException
*/
private void assignKeysToParamMapList(Configuration configuration, ResultSet rs, ResultSetMetaData rsmd,
String[] keyProperties, ArrayList<ParamMap<?>> paramMapList) throws SQLException {
Iterator<ParamMap<?>> iterator = paramMapList.iterator();
List<KeyAssigner> assignerList = new ArrayList<>();
long counter = 0;
while (rs.next()) {
if (!iterator.hasNext()) {
throw new ExecutorException(String.format(MSG_TOO_MANY_KEYS, counter));
}
ParamMap<?> paramMap = iterator.next();
if (assignerList.isEmpty()) {
for (int i = 0; i < keyProperties.length; i++) {
assignerList
.add(getAssignerForParamMap(configuration, rsmd, i + 1, paramMap, keyProperties[i], keyProperties, false)
.getValue());
}
}
assignerList.forEach(x -> x.assign(rs, paramMap));
counter++;
}
}
/**
* 处理 Map 类型，遍历数据库生成的主键结果集，并设置到 Parameters 集合对应的元素的属性中
* @param configuration
* @param rs
* @param rsmd
* @param keyProperties
* @param paramMap
* @throws SQLException
*/
private void assignKeysToParamMap(Configuration configuration, ResultSet rs, ResultSetMetaData rsmd,
String[] keyProperties, Map<String, ?> paramMap) throws SQLException {
if (paramMap.isEmpty()) {
return;
}
Map<String, Entry<Iterator<?>, List<KeyAssigner>>> assignerMap = new HashMap<>();
for (int i = 0; i < keyProperties.length; i++) {
Entry<String, KeyAssigner> entry = getAssignerForParamMap(configuration, rsmd, i + 1, paramMap, keyProperties[i],
keyProperties, true);
Entry<Iterator<?>, List<KeyAssigner>> iteratorPair = assignerMap.computeIfAbsent(entry.getKey(),
k -> entry(collectionize(paramMap.get(k)).iterator(), new ArrayList<>()));
iteratorPair.getValue().add(entry.getValue());
}
long counter = 0;
while (rs.next()) {
for (Entry<Iterator<?>, List<KeyAssigner>> pair : assignerMap.values()) {
if (!pair.getKey().hasNext()) {
throw new ExecutorException(String.format(MSG_TOO_MANY_KEYS, counter));
}
Object param = pair.getKey().next();
pair.getValue().forEach(x -> x.assign(rs, param));
}
counter++;
}
}
private Entry<String, KeyAssigner> getAssignerForParamMap(Configuration config, ResultSetMetaData rsmd,
int columnPosition, Map<String, ?> paramMap, String keyProperty, String[] keyProperties, boolean omitParamName) {
boolean singleParam = paramMap.values().stream().distinct().count() == 1;
int firstDot = keyProperty.indexOf('.');
if (firstDot == -1) {
if (singleParam) {
return getAssignerForSingleParam(config, rsmd, columnPosition, paramMap, keyProperty, omitParamName);
}
throw new ExecutorException("Could not determine which parameter to assign generated keys to. "
+ "Note that when there are multiple parameters, 'keyProperty' must include the parameter name (e.g. 'param.id'). "
+ "Specified key properties are " + ArrayUtil.toString(keyProperties) + " and available parameters are "
+ paramMap.keySet());
}
String paramName = keyProperty.substring(0, firstDot);
if (paramMap.containsKey(paramName)) {
String argParamName = omitParamName ? null : paramName;
String argKeyProperty = keyProperty.substring(firstDot + 1);
return entry(paramName, new KeyAssigner(config, rsmd, columnPosition, argParamName, argKeyProperty));
} else if (singleParam) {
return getAssignerForSingleParam(config, rsmd, columnPosition, paramMap, keyProperty, omitParamName);
} else {
throw new ExecutorException("Could not find parameter '" + paramName + "'. "
+ "Note that when there are multiple parameters, 'keyProperty' must include the parameter name (e.g. 'param.id'). "
+ "Specified key properties are " + ArrayUtil.toString(keyProperties) + " and available parameters are "
+ paramMap.keySet());
}
}
private Entry<String, KeyAssigner> getAssignerForSingleParam(Configuration config, ResultSetMetaData rsmd,
int columnPosition, Map<String, ?> paramMap, String keyProperty, boolean omitParamName) {
// Assume 'keyProperty' to be a property of the single param.
String singleParamName = nameOfSingleParam(paramMap);
String argParamName = omitParamName ? null : singleParamName;
return entry(singleParamName, new KeyAssigner(config, rsmd, columnPosition, argParamName, keyProperty));
}
private static String nameOfSingleParam(Map<String, ?> paramMap) {
// There is virtually one parameter, so any key works.
return paramMap.keySet().iterator().next();
}
/**
* 参数对象集合化
* @param param
* @return
*/
private static Collection<?> collectionize(Object param) {
if (param instanceof Collection) {
return (Collection<?>) param;
} else if (param instanceof Object[]) {
return Arrays.asList((Object[]) param);
} else {
return Arrays.asList(param);
}
}
private static <K, V> Entry<K, V> entry(K key, V value) {
// Replace this with Map.entry(key, value) in Java 9.
return new AbstractMap.SimpleImmutableEntry<>(key, value);
}
private class KeyAssigner {
private final Configuration configuration;
private final ResultSetMetaData rsmd;
private final TypeHandlerRegistry typeHandlerRegistry;
private final int columnPosition;
private final String paramName;
private final String propertyName;
private TypeHandler<?> typeHandler;
protected KeyAssigner(Configuration configuration, ResultSetMetaData rsmd, int columnPosition, String paramName,
String propertyName) {
super();
this.configuration = configuration;
this.rsmd = rsmd;
this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
this.columnPosition = columnPosition;
this.paramName = paramName;
this.propertyName = propertyName;
}
protected void assign(ResultSet rs, Object param) {
if (paramName != null) {
// If paramName is set, param is ParamMap
param = ((ParamMap<?>) param).get(paramName);
}
MetaObject metaParam = configuration.newMetaObject(param);
try {
if (typeHandler == null) {
if (metaParam.hasSetter(propertyName)) {
Class<?> propertyType = metaParam.getSetterType(propertyName);
typeHandler = typeHandlerRegistry.getTypeHandler(propertyType,
JdbcType.forCode(rsmd.getColumnType(columnPosition)));
} else {
throw new ExecutorException("No setter found for the keyProperty '" + propertyName + "' in '"
+ metaParam.getOriginalObject().getClass().getName() + "'.");
}
}
if (typeHandler == null) {
// Error?
} else {
Object value = typeHandler.getResult(rs, columnPosition);
metaParam.setValue(propertyName, value);
}
} catch (SQLException e) {
throw new ExecutorException("Error getting generated key or setting result to parameter object. Cause: " + e,
e);
}
}
}
}
mapper 配置
<insert id="test_insert" useGeneratedKeys="true" keyProperty＝”id”〉
INSERT INTO t_user(username , pwd) VALUES
<foreach item= "item" collection=” list” separator=”,”>
(#(item.username}, #(item.pwd})
</foreach>
</insert>
整个示例的执行流程
image.png
SelectKeyGenerator
对于不支持自动生成自增主键的数据库，例如 Oracle 数据库，用户可以利用 MyBatis 提供 的 SelectkeyGenerator 来生成主键， SelectKeyGenerator 也可以实现类似于 Jdbc3KeyGenerator 提供的、获取数据库自动生成的主键的功能。
SelectKeyGenerator 主要用于生成主键，它会执行映射配置文件中定义的＜selectKey＞节点的 SQL 语句，该语句会获取 insert 语句所需要的主键。
mapper 配置
<insert id="insertAuthor" parameterType="org.apache.ibatis.domain.blog.Author">
<selectKey keyProperty="id" resultType="_int" order="BEFORE">
<include refid="selectNum">
<property name="num" value="1"/>
</include>
</selectKey>
insert into Author (username,password,email,bio)
values (#{username},#{password},#{email},#{bio})
</insert>
<sql id="selectNum">
SELECT #{num}
</sql>
调用方法地方
XMLStatementBuilder.parseStatementNode() 方法中的 processSelectKeyNodes() 方法，用来解析 mapper.xml 文件中 insert 节点中的 <selectKey> ，主要用来生成 Id 主键。
// Parse selectKey after includes and remove them.
// 处理＜selectKey> 节点,来解决主键自增问题，
processSelectKeyNodes(id, parameterTypeClass, langDriver);
/**
* 解析 <selectKey> 节点
* @param id
* @param parameterTypeClass
* @param langDriver
*/
private void processSelectKeyNodes(String id, Class<?> parameterTypeClass, LanguageDriver langDriver) {
// 获取全部的 <selectKey> 节点
List<XNode> selectKeyNodes = context.evalNodes("selectKey");
// 解析＜selectKey＞节点
if (configuration.getDatabaseId() != null) {
parseSelectKeyNodes(id, selectKeyNodes, parameterTypeClass, langDriver, configuration.getDatabaseId());
}
parseSelectKeyNodes(id, selectKeyNodes, parameterTypeClass, langDriver, null);
// 移除＜selectKey＞节点
removeSelectKeyNodes(selectKeyNodes);
}
/**
* 解析 <selectKey> 节点
* @param parentId
* @param list
* @param parameterTypeClass
* @param langDriver
* @param skRequiredDatabaseId
*/
private void parseSelectKeyNodes(String parentId, List<XNode> list, Class<?> parameterTypeClass, LanguageDriver langDriver, String skRequiredDatabaseId) {
for (XNode nodeToHandle : list) {
String id = parentId + SelectKeyGenerator.SELECT_KEY_SUFFIX;
String databaseId = nodeToHandle.getStringAttribute("databaseId");
if (databaseIdMatchesCurrent(id, databaseId, skRequiredDatabaseId)) {
parseSelectKeyNode(id, nodeToHandle, parameterTypeClass, langDriver, databaseId);
}
}
}
/**
* 解析 <selectKey> 节点
* @param id
* @param nodeToHandle
* @param parameterTypeClass
* @param langDriver
* @param databaseId
*/
private void parseSelectKeyNode(String id, XNode nodeToHandle, Class<?> parameterTypeClass, LanguageDriver langDriver, String databaseId) {
// 获取 <selectKey> 节点的多个属性
String resultType = nodeToHandle.getStringAttribute("resultType");
Class<?> resultTypeClass = resolveClass(resultType);
StatementType statementType = StatementType.valueOf(nodeToHandle.getStringAttribute("statementType", StatementType.PREPARED.toString()));
String keyProperty = nodeToHandle.getStringAttribute("keyProperty");
String keyColumn = nodeToHandle.getStringAttribute("keyColumn");
boolean executeBefore = "BEFORE".equals(nodeToHandle.getStringAttribute("order", "AFTER"));
//defaults
boolean useCache = false;
boolean resultOrdered = false;
KeyGenerator keyGenerator = NoKeyGenerator.INSTANCE;
Integer fetchSize = null;
Integer timeout = null;
boolean flushCache = false;
String parameterMap = null;
String resultMap = null;
ResultSetType resultSetTypeEnum = null;
// 通过 LanguageDriver.createSqlSource() 方法生成 SqlSource
SqlSource sqlSource = langDriver.createSqlSource(configuration, nodeToHandle, parameterTypeClass);
// <selectKey> 节点中只能配置 select 吾句
SqlCommandType sqlCommandType = SqlCommandType.SELECT;
// 创建 MappedStatement 对象，并保存到 Configuration.mappedStatements 集合
builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, null);
id = builderAssistant.applyCurrentNamespace(id, false);
MappedStatement keyStatement = configuration.getMappedStatement(id, false);
// 创建 <selectKey> 节点对应的 KeyGenerator,添加到 Configuration.keyGenerators 集合;
configuration.addKeyGenerator(id, new SelectKeyGenerator(keyStatement, executeBefore));
}
public class SelectKeyGenerator implements KeyGenerator {
public static final String SELECT_KEY_SUFFIX = "!selectKey";
// 标识 <selectKey＞节点中定义的 SQL 语句是在 insert 吾句之前执行还是之后执行
private final boolean executeBefore;
private final MappedStatement keyStatement;
public SelectKeyGenerator(MappedStatement keyStatement, boolean executeBefore) {
this.executeBefore = executeBefore;
this.keyStatement = keyStatement;
}
@Override
public void processBefore(Executor executor, MappedStatement ms, Statement stmt, Object parameter) {
if (executeBefore) {
processGeneratedKeys(executor, ms, parameter);
}
}
@Override
public void processAfter(Executor executor, MappedStatement ms, Statement stmt, Object parameter) {
if (!executeBefore) {
processGeneratedKeys(executor, ms, parameter);
}
}
/**
* <insert id="insert">
* <!-- 在 insert 语句执行之前，先通过执行 <selectKey＞节点对应的 Select 语句生成 insert 语句中使用的主键，也就是这里的 id -->
* <selectKey keyProperty=”id” result Type=” int” order=” BEFORE” >
* SELECT FLOOR(RAND() * 10000) ;
* </selectKey>
* insert into T_USER (ID , username ,pwd) values ( #{id} , #{username} , #{pwd) )
* </insert>
*/
/**
* processGeneratedKeys() 方法会执行＜selectKey＞节点中配置的 SQL 语句，获取 insert 语句中用到的主键井映射成对象，然后按照配置，将主键对象中对应的属性设置到用户参数中。
* @param executor
* @param ms
* @param parameter
*/
private void processGeneratedKeys(Executor executor, MappedStatement ms, Object parameter) {
try {
if (parameter != null && keyStatement != null && keyStatement.getKeyProperties() != null) {
// 获取 selectKey 节点的 keyProperties 配置的属性名称，它表示主键对应的属性
String[] keyProperties = keyStatement.getKeyProperties();
final Configuration configuration = ms.getConfiguration();
// 创建用户传入的实参对象对应的 metaObject 对象
final MetaObject metaParam = configuration.newMetaObject(parameter);
// Do not close keyExecutor.
// The transaction will be closed by parent executor.
// 创建 Executor 对象，并执行 keyStatement 字段中记录的 SQL 语句，并得到 主键对象
Executor keyExecutor = configuration.newExecutor(executor.getTransaction(), ExecutorType.SIMPLE);
List<Object> values = keyExecutor.query(keyStatement, parameter, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER);
// 检测 values 集合的长度，该集合长度只能为 1
if (values.size() == 0) {
throw new ExecutorException("SelectKey returned no data.");
} else if (values.size() > 1) {
throw new ExecutorException("SelectKey returned more than one value.");
} else {
MetaObject metaResult = configuration.newMetaObject(values.get(0));
if (keyProperties.length == 1) {
if (metaResult.hasGetter(keyProperties[0])) {
// 从主键对象中获取指定属性，设直到用户参数的对应属性中
setValue(metaParam, keyProperties[0], metaResult.getValue(keyProperties[0]));
} else {
// no getter for the property - maybe just a single value object
// so try that
//如采主键对象不包含指定属性的 setter 方法，可能是一个基本类型，直接将主键对象设置到用户参数中
setValue(metaParam, keyProperties[0], values.get(0));
}
} else {
// 处理主键有多列的情况，其实现是从主键对象中取出指定属性，并设直到用户参数的对应属性中
handleMultipleProperties(keyProperties, metaParam, metaResult);
}
}
}
} catch (ExecutorException e) {
throw e;
} catch (Exception e) {
throw new ExecutorException("Error selecting key or setting result to parameter object. Cause: " + e, e);
}
}
private void handleMultipleProperties(String[] keyProperties,
MetaObject metaParam, MetaObject metaResult) {
String[] keyColumns = keyStatement.getKeyColumns();
if (keyColumns == null || keyColumns.length == 0) {
// no key columns specified, just use the property names
for (String keyProperty : keyProperties) {
setValue(metaParam, keyProperty, metaResult.getValue(keyProperty));
}
} else {
if (keyColumns.length != keyProperties.length) {
throw new ExecutorException("If SelectKey has key columns, the number must match the number of key properties.");
}
for (int i = 0; i < keyProperties.length; i++) {
setValue(metaParam, keyProperties[i], metaResult.getValue(keyColumns[i]));
}
}
}
private void setValue(MetaObject metaParam, String property, Object value) {
if (metaParam.hasSetter(property)) {
metaParam.setValue(property, value);
} else {
throw new ExecutorException("No setter found for the keyProperty '" + property + "' in " + metaParam.getOriginalObject().getClass().getName() + ".");
}
}
}
mapper 配置
<insert id="insert">
<!-- 在 insert 语句执行之前，先通过执行 <selectKey＞节点对应的 Select 语句生成 insert 语句中使用的主键，也就是这里的 id -->
<selectKey keyProperty=”id” result Type=” int” order=” BEFORE” >
SELECT FLOOR(RAND()10000) ;
</selectKey>
insert into T_USER (ID , username ,pwd) values ( #{id} , #{username} , #{pwd) )
</insert>
整个示例的执行流程
image.png
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