XMLStatementBuilder.java

/*
 *    Copyright 2009-2014 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.builder.xml;

import java.util.List;
import java.util.Locale;

import org.apache.ibatis.builder.BaseBuilder;
import org.apache.ibatis.builder.MapperBuilderAssistant;
import org.apache.ibatis.executor.keygen.Jdbc3KeyGenerator;
import org.apache.ibatis.executor.keygen.KeyGenerator;
import org.apache.ibatis.executor.keygen.NoKeyGenerator;
import org.apache.ibatis.executor.keygen.SelectKeyGenerator;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ResultSetType;
import org.apache.ibatis.mapping.SqlCommandType;
import org.apache.ibatis.mapping.SqlSource;
import org.apache.ibatis.mapping.StatementType;
import org.apache.ibatis.parsing.XNode;
import org.apache.ibatis.scripting.LanguageDriver;
import org.apache.ibatis.session.Configuration;

/**
 * @author Clinton Begin
 */
/**
 * XML语句构建器，建造者模式,继承BaseBuilder
 *
 */
public class XMLStatementBuilder extends BaseBuilder {

  private MapperBuilderAssistant builderAssistant;
  private XNode context;
  private String requiredDatabaseId;

  public XMLStatementBuilder(Configuration configuration, MapperBuilderAssistant builderAssistant, XNode context) {
    this(configuration, builderAssistant, context, null);
  }

  public XMLStatementBuilder(Configuration configuration, MapperBuilderAssistant builderAssistant, XNode context, String databaseId) {
    super(configuration);
    this.builderAssistant = builderAssistant;
    this.context = context;
    this.requiredDatabaseId = databaseId;
  }

  //解析语句(select|insert|update|delete)
//<select
//  id="selectPerson"
//  parameterType="int"
//  parameterMap="deprecated"
//  resultType="hashmap"
//  resultMap="personResultMap"
//  flushCache="false"
//  useCache="true"
//  timeout="10000"
//  fetchSize="256"
//  statementType="PREPARED"
//  resultSetType="FORWARD_ONLY">
//  SELECT * FROM PERSON WHERE ID = #{id}
//</select>
  public void parseStatementNode() {
    String id = context.getStringAttribute("id");
    String databaseId = context.getStringAttribute("databaseId");

    //如果databaseId不匹配，退出
    if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
      return;
    }

    //暗示驱动程序每次批量返回的结果行数
    Integer fetchSize = context.getIntAttribute("fetchSize");
    //超时时间
    Integer timeout = context.getIntAttribute("timeout");
    //引用外部 parameterMap,已废弃
    String parameterMap = context.getStringAttribute("parameterMap");
    //参数类型
    String parameterType = context.getStringAttribute("parameterType");
    Class<?> parameterTypeClass = resolveClass(parameterType);
    //引用外部的 resultMap(高级功能)
    String resultMap = context.getStringAttribute("resultMap");
    //结果类型
    String resultType = context.getStringAttribute("resultType");
    //脚本语言,mybatis3.2的新功能
    String lang = context.getStringAttribute("lang");
    //得到语言驱动
    LanguageDriver langDriver = getLanguageDriver(lang);

    Class<?> resultTypeClass = resolveClass(resultType);
    //结果集类型，FORWARD_ONLY|SCROLL_SENSITIVE|SCROLL_INSENSITIVE 中的一种
    String resultSetType = context.getStringAttribute("resultSetType");
    //语句类型, STATEMENT|PREPARED|CALLABLE 的一种
    StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
    ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);

    //获取命令类型(select|insert|update|delete)
    String nodeName = context.getNode().getNodeName();
    SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
    boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
    boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
    //是否要缓存select结果
    boolean useCache = context.getBooleanAttribute("useCache", isSelect);
    //仅针对嵌套结果 select 语句适用：如果为 true，就是假设包含了嵌套结果集或是分组了，这样的话当返回一个主结果行的时候，就不会发生有对前面结果集的引用的情况。
    //这就使得在获取嵌套的结果集的时候不至于导致内存不够用。默认值：false。 
    boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);

    // Include Fragments before parsing
    //解析之前先解析<include>SQL片段
    XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
    includeParser.applyIncludes(context.getNode());

    // Parse selectKey after includes and remove them.
    //解析之前先解析<selectKey>
    processSelectKeyNodes(id, parameterTypeClass, langDriver);
    
    // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
    //解析成SqlSource，一般是DynamicSqlSource
    SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
    String resultSets = context.getStringAttribute("resultSets");
    //(仅对 insert 有用) 标记一个属性, MyBatis 会通过 getGeneratedKeys 或者通过 insert 语句的 selectKey 子元素设置它的值
    String keyProperty = context.getStringAttribute("keyProperty");
    //(仅对 insert 有用) 标记一个属性, MyBatis 会通过 getGeneratedKeys 或者通过 insert 语句的 selectKey 子元素设置它的值
    String keyColumn = context.getStringAttribute("keyColumn");
    KeyGenerator keyGenerator;
    String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
    keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
    if (configuration.hasKeyGenerator(keyStatementId)) {
      keyGenerator = configuration.getKeyGenerator(keyStatementId);
    } else {
      keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
          configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
          ? new Jdbc3KeyGenerator() : new NoKeyGenerator();
    }

	//又去调助手类
    builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
        fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
        resultSetTypeEnum, flushCache, useCache, resultOrdered, 
        keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
  }

  private void processSelectKeyNodes(String id, Class<?> parameterTypeClass, LanguageDriver langDriver) {
    List<XNode> selectKeyNodes = context.evalNodes("selectKey");
    if (configuration.getDatabaseId() != null) {
      parseSelectKeyNodes(id, selectKeyNodes, parameterTypeClass, langDriver, configuration.getDatabaseId());
    }
    parseSelectKeyNodes(id, selectKeyNodes, parameterTypeClass, langDriver, null);
    removeSelectKeyNodes(selectKeyNodes);
  }

  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);
      }
    }
  }

  private void parseSelectKeyNode(String id, XNode nodeToHandle, Class<?> parameterTypeClass, LanguageDriver langDriver, String databaseId) {
    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 = new NoKeyGenerator();
    Integer fetchSize = null;
    Integer timeout = null;
    boolean flushCache = false;
    String parameterMap = null;
    String resultMap = null;
    ResultSetType resultSetTypeEnum = null;

    SqlSource sqlSource = langDriver.createSqlSource(configuration, nodeToHandle, parameterTypeClass);
    SqlCommandType sqlCommandType = SqlCommandType.SELECT;

    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);
    configuration.addKeyGenerator(id, new SelectKeyGenerator(keyStatement, executeBefore));
  }

  private void removeSelectKeyNodes(List<XNode> selectKeyNodes) {
    for (XNode nodeToHandle : selectKeyNodes) {
      nodeToHandle.getParent().getNode().removeChild(nodeToHandle.getNode());
    }
  }

  private boolean databaseIdMatchesCurrent(String id, String databaseId, String requiredDatabaseId) {
    if (requiredDatabaseId != null) {
      if (!requiredDatabaseId.equals(databaseId)) {
        return false;
      }
    } else {
      if (databaseId != null) {
        return false;
      }
      // skip this statement if there is a previous one with a not null databaseId
      id = builderAssistant.applyCurrentNamespace(id, false);
      if (this.configuration.hasStatement(id, false)) {
        MappedStatement previous = this.configuration.getMappedStatement(id, false); // issue #2
        if (previous.getDatabaseId() != null) {
          return false;
        }
      }
    }
    return true;
  }

  //取得语言驱动
  private LanguageDriver getLanguageDriver(String lang) {
    Class<?> langClass = null;
    if (lang != null) {
      langClass = resolveClass(lang);
    }
    //调用builderAssistant
    return builderAssistant.getLanguageDriver(langClass);
  }

}