/// <summary>
/// 向多表查询中添加一个联合查询的表.
/// </summary>
/// <typeparam name="TEntityAgent">表的实体映射代理对象.</typeparam>
/// <returns></returns>
public EntityJoinSelector Join <TEntityAgent>() where TEntityAgent : EntityAgent, new()
{
if (sBlock == null)
{
throw new NullReferenceException("Please invoke in advance the \"From\" method.");
}
TEntityAgent agent = new TEntityAgent();
TableMapper context = agent.CreateContext();
context.SetDataEngine(ReadEngine, null);
agent.TableContext = context;
agent.IncludeTableName = true; // 指法查询代理对象在生成字段信息时带上表名.
// 将实体表的代理类记录下来，后面组织查询时还要用到.
if (!(AgentsIndexes.ContainsKey(typeof(TEntityAgent))))
{
AgentBufferItem BufferItem = new AgentBufferItem(agent);
AgentsIndexes.Add(typeof(TEntityAgent), BufferItem);
Agents.Add(BufferItem);
}
// 向 FROM 子向中添加 LEFT JOIN 子句.
EntityTableAttribute tableAttribute = context.GetTableAttribute();
LeftJoinDescription leftJoin = fm.LeftJoin(fm.Table(tableAttribute.TableName));
fBlock.Content.Add(leftJoin);
// 返回 JEFT JOIN 子句的筛选器构建对象.
return(new EntityJoinSelector(this, leftJoin, (t) => {
if (AgentsIndexes.ContainsKey(t))
{
return AgentsIndexes[t].Agent <EntityAgent>();
}
return null;
}));
}
/// <summary>
/// 开始建立查询命令对象树.
/// </summary>
/// <typeparam name="TEntityAgent">表对应的实体映射代理对象.</typeparam>
/// <returns></returns>
internal MultiQuerySelector From <TEntityAgent>() where TEntityAgent : EntityAgent, new()
{
sBlock = Command.Select();
TEntityAgent agent = new TEntityAgent();
TableMapper context = agent.CreateContext();
context.SetDataEngine(ReadEngine, null);
agent.TableContext = context;
agent.IncludeTableName = true; // 指法查询代理对象在生成字段信息时带上表名.
// 将实体表的代理类记录下来，后面组织查询时还要用到.
if (!(AgentsIndexes.ContainsKey(typeof(TEntityAgent))))
{
AgentBufferItem BufferItem = new AgentBufferItem(agent);
AgentsIndexes.Add(typeof(TEntityAgent), BufferItem);
Agents.Add(BufferItem);
}
// 向 FROM 了向中添加查询的表.
EntityTableAttribute tableAttribute = context.GetTableAttribute();
fBlock.Content.Add(fm.Table(tableAttribute.TableName));
sBlock.Blocks.Add(fBlock);
return(this);
}
