mybatis中KeyGenerator的设计与实现

key Generator主要是用于insert操作，其接口定义为

public interface KeyGenerator {

  void processBefore(Executor executor, MappedStatement ms, Statement stmt, Object parameter);

  void processAfter(Executor executor, MappedStatement ms, Statement stmt, Object parameter);

}

其相关类层次图为

1、keyGenerator相关的配置

全局配置useGeneratedKeys，默认是false

局部配置,对于某条sql语句，useGeneratedKeys

当局部配置没有配置时，在全局配置并且命令为insert才有效

2、 selectKey结点与相关KeyGenerator关系

selectKey主要是对于不支持自动生成主键时的处理。这种情况使用的是SelectKeyGenerator,通过调用processBefore来生成主键，而对于可以生成主键的，主要是通过processAfter来处理

//BaseStatementHandler  
protected void generateKeys(Object parameter) {
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    ErrorContext.instance().store();
    keyGenerator.processBefore(executor, mappedStatement, null, parameter);
    ErrorContext.instance().recall();
  }

3、 KeyGenerator的调用

在sql语句执行后的处理，主要是在CallableStatementHandler、 PreparedStatementHandler、 SimpleStatementHandler中的update中执行sql后的处理

// CallableStatementHandler
public int update(Statement statement) throws SQLException {
    CallableStatement cs = (CallableStatement) statement;
    cs.execute();
    int rows = cs.getUpdateCount();
    Object parameterObject = boundSql.getParameterObject();
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    keyGenerator.processAfter(executor, mappedStatement, cs, parameterObject);
    resultSetHandler.handleOutputParameters(cs);
    return rows;
  }

// PreparedStatementHandler
public int update(Statement statement) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();
    int rows = ps.getUpdateCount();
    Object parameterObject = boundSql.getParameterObject();
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);
    return rows;
  }

// SimpleStatementHandler
public int update(Statement statement) throws SQLException {
    String sql = boundSql.getSql();
    Object parameterObject = boundSql.getParameterObject();
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    int rows;
    if (keyGenerator instanceof Jdbc3KeyGenerator) {
      statement.execute(sql, Statement.RETURN_GENERATED_KEYS);
      rows = statement.getUpdateCount();
      keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject);
    } else if (keyGenerator instanceof SelectKeyGenerator) {
      statement.execute(sql);
      rows = statement.getUpdateCount();
      keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject);
    } else {
      statement.execute(sql);
      rows = statement.getUpdateCount();
    }
    return rows;
  }

4、Jdbc3KeyGenerator的实现

其主要是针对支持主键自动生成的数据库。在处理主键时，分参数类型

（1）如果是ParaMap或者StrictMap时，对于单参数时，以Map的任意一个key作为参数名来构建 String到KeyAssigner的实体对

（2）如果参数是ArrayList并且非空，元素是ParaMap时

（3）单参数并且没有@Param注解

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);
    }
  }

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) {
    Set<String> keySet = paramMap.keySet();
    // A caveat : if the only parameter has {@code @Param("param2")} on it,
    // it must be referenced with param name e.g. 'param2.x'.
    boolean singleParam = !keySet.contains(SECOND_GENERIC_PARAM_NAME);
    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 "
          + keySet);
    }
    String paramName = keyProperty.substring(0, firstDot);
    if (keySet.contains(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 "
          + 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 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++;
    }
  }

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));
    }
  }

原文链接：https://blog.csdn.net/wuli2496/article/details/108939622

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