改写步骤图

image.png

书接上文

获取完路由上下文后，从prepare方法中来到了executeRewrite方法，其源码如下：

  1.     private Collection<ExecutionUnit> executeRewrite(String sql, List<Object> parameters, RouteContext routeContext) {
  2.         this.registerRewriteDecorator();
  3.         SQLRewriteContext sqlRewriteContext = this.rewriter.createSQLRewriteContext(sql, parameters, routeContext.getSqlStatementContext(), routeContext);
  4.         return routeContext.getRouteResult().getRouteUnits().isEmpty() ? this.rewrite(sqlRewriteContext) : this.rewrite(routeContext, sqlRewriteContext);
  5.     }

显然，这个方法中进行了SQL改写（rewrite），这正是本节的重点，以下的分析将会围绕着这个方法进行展开。

注册

实现，先进行了重写装饰器的注册，该方法源码如下：
image.png
即在SQLRewriteEntry中注册SQLRewriteContextDecorator的对象。

createSQLRewriteContext

回到executeRewrite方法中，在执行完registerRewriteDecorator后将会调用createSQLRewriteContext，这里根据语义判断应该是创建SQLRewrite的上下文，其源码如下：
image.png

decorate

  1.     private void decorate(Map<BaseRule, SQLRewriteContextDecorator> decorators, SQLRewriteContext sqlRewriteContext, RouteContext routeContext) {
  2.         BaseRule rule;
  3.         SQLRewriteContextDecorator decorator;
  4.         for(Iterator var4 = decorators.entrySet().iterator(); var4.hasNext(); decorator.decorate(rule, this.properties, sqlRewriteContext)) {
  5.             Entry<BaseRule, SQLRewriteContextDecorator> entry = (Entry)var4.next();
  6.             rule = (BaseRule)entry.getKey();
  7.             decorator = (SQLRewriteContextDecorator)entry.getValue();
  8.             if (decorator instanceof RouteContextAware) {
  9.                 ((RouteContextAware)decorator).setRouteContext(routeContext);
  10.             }
  11.         }
  13.     }

继续追：

  1.     public void decorate(ShardingRule shardingRule, ConfigurationProperties properties, SQLRewriteContext sqlRewriteContext) {
  2.         Iterator var4 = (new ShardingParameterRewriterBuilder(shardingRule, this.routeContext)).getParameterRewriters(sqlRewriteContext.getSchemaMetaData()).iterator();
  4.         while(var4.hasNext()) {
  5.             ParameterRewriter each = (ParameterRewriter)var4.next();
  6.             if (!sqlRewriteContext.getParameters().isEmpty() && each.isNeedRewrite(sqlRewriteContext.getSqlStatementContext())) {
  7.                 each.rewrite(sqlRewriteContext.getParameterBuilder(), sqlRewriteContext.getSqlStatementContext(), sqlRewriteContext.getParameters());
  8.             }
  9.         }
  11.         sqlRewriteContext.addSQLTokenGenerators((new ShardingTokenGenerateBuilder(shardingRule, this.routeContext)).getSQLTokenGenerators());
  12.     }

这里判断一下是否需要重写且参数为空，如果是则进行重写。
image.png
即把所有的重写结果放入到sqlRewrite上下文中。

rewrite

返回到executeRewrite，这里进行了的上下文信息已经装填完成：
image.png
即将开始真正的重写。
image.png
其源码如下：

  1.     private Collection<ExecutionUnit> rewrite(RouteContext routeContext, SQLRewriteContext sqlRewriteContext) {
  2.         Collection<ExecutionUnit> result = new LinkedHashSet();
  3.         Iterator var4 = (new SQLRouteRewriteEngine()).rewrite(sqlRewriteContext, routeContext.getRouteResult()).entrySet().iterator();
  5.         while(var4.hasNext()) {
  6.             Entry<RouteUnit, SQLRewriteResult> entry = (Entry)var4.next();
  7.             result.add(new ExecutionUnit(((RouteUnit)entry.getKey()).getDataSourceMapper().getActualName(), new SQLUnit(((SQLRewriteResult)entry.getValue()).getSql(), ((SQLRewriteResult)entry.getValue()).getParameters())));
  8.         }
  10.         return result;
  11.     }

继续追踪：

  1.     public Map<RouteUnit, SQLRewriteResult> rewrite(SQLRewriteContext sqlRewriteContext, RouteResult routeResult) {
  2.         Map<RouteUnit, SQLRewriteResult> result = new LinkedHashMap(routeResult.getRouteUnits().size(), 1.0F);
  3.         Iterator var4 = routeResult.getRouteUnits().iterator();
  5.         while(var4.hasNext()) {
  6.             RouteUnit each = (RouteUnit)var4.next();
  7.             result.put(each, new SQLRewriteResult((new RouteSQLBuilder(sqlRewriteContext, each)).toSQL(), this.getParameters(sqlRewriteContext.getParameterBuilder(), routeResult, each)));
  8.         }
  10.         return result;
  11.     }

这里具体是根据RouteUnit的分组进行重写（字符串拼接），详细代码在toSQL中，其源码如下：

  1.     public final String toSQL() {
  2.         if (this.context.getSqlTokens().isEmpty()) {
  3.             return this.context.getSql();
  4.         } else {
  5.             Collections.sort(this.context.getSqlTokens());
  6.             StringBuilder result = new StringBuilder();
  7.             result.append(this.context.getSql().substring(0, ((SQLToken)this.context.getSqlTokens().get(0)).getStartIndex()));
  8.             Iterator var2 = this.context.getSqlTokens().iterator();
  10.             while(var2.hasNext()) {
  11.                 SQLToken each = (SQLToken)var2.next();
  12.                 result.append(this.getSQLTokenText(each));
  13.                 result.append(this.getConjunctionText(each));
  14.             }
  16.             return result.toString();
  17.         }
  18.     }

经过字符串拼接得出结果：
image.png

总结

最终拼凑好的语句信息都放在了ExecutionUnit和SQLUnit中：image.png