/// <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>
/// 解释 LEFT JOIN 子句。
/// </summary>
/// <param name="DbParameters">用于缓存在解释过程中可能会产生的参数。</param>
/// <returns></returns>
public override string Parsing(ref List <IDbDataParameter> DbParameters)
{
LeftJoinDescription LeftJoin = (LeftJoinDescription)this.Description;
StringBuilder cBuffer = new StringBuilder(" LEFT JOIN");
LeftJoin.Table.DescriptionParserAdapter = LeftJoin.DescriptionParserAdapter;
cBuffer.Append(LeftJoin.Table.GetParser().Parsing(ref DbParameters));
cBuffer.Append(" ON");
ExpDescription ExpDes = (ExpDescription)LeftJoin.OnDescription[0];
ExpDes.DescriptionParserAdapter = LeftJoin.DescriptionParserAdapter;
cBuffer.Append(ExpDes.GetParser().Parsing(ref DbParameters));
if (LeftJoin.OnDescription.Count > 1)
{
for (int i = 1; i < LeftJoin.OnDescription.Count; ++i)
{
ExpDes = (ExpDescription)LeftJoin.OnDescription[i];
ExpDes.DescriptionParserAdapter = LeftJoin.DescriptionParserAdapter;
cBuffer.AppendFormat(" {0} {1}", KeywordsAnd, ExpDes.GetParser().Parsing(ref DbParameters));
}
}
return(cBuffer.ToString());
}
/// <summary>
///
/// </summary>
/// <param name="owner"></param>
/// <param name="leftJion"></param>
/// <param name="getAgent"></param>
internal EntityJoinSelector(MultiQuerySelector owner, LeftJoinDescription leftJion, Func <Type, EntityAgent> getAgent)
{
_Owner = owner;
LeftJion = leftJion;
GetTargetAgent = getAgent;
}