/// <summary>
/// <para>从指定的表标识对应的实体开始进行路径展开。</para>
/// <para>注：展开过程包括对父实体的属性集的搜索。</para>
/// </summary>
/// <param name="table">指定的进行展开的起点。</param>
/// <param name="path">指定要展开的成员路径，支持多级导航属性路径。</param>
/// <param name="step">指定路径中每个属性的展开回调函数。</param>
/// <returns>返回找到的结果。</returns>
public static ReduceResult Reduce(this TableIdentifier table, string path, Func <ReduceContext, ISource> step = null)
{
if (table == null)
{
throw new ArgumentNullException(nameof(table));
}
if (table.Entity == null)
{
throw new DataException($"The '{table}' table cannot be expanded.");
}
if (string.IsNullOrEmpty(path))
{
return(ReduceResult.Failure(table));
}
ICollection <IEntityMetadata> ancestors = null;
IEntityPropertyMetadata property = null;
ISource token = table;
var parts = path.Split('.');
var properties = table.Entity.Properties;
for (int i = 0; i < parts.Length; i++)
{
if (properties == null)
{
return(ReduceResult.Failure(token));
}
//如果当前属性集合中不包含指定的属性，则尝试从父实体中查找
if (!properties.TryGet(parts[i], out property))
{
//尝试从父实体中查找指定的属性
property = FindBaseProperty(ref properties, parts[i], ref ancestors);
//如果父实体中也不含指定的属性则返回失败
if (property == null)
{
return(ReduceResult.Failure(token));
}
}
//如果回调函数不为空，则调用匹配回调函数
//注意：将回调函数返回的结果作为下一次的用户数据保存起来
if (step != null)
{
token = step(new ReduceContext(string.Join(".", parts, 0, i), token, property, ancestors));
}
//清空继承实体链
if (ancestors != null)
{
ancestors.Clear();
}
if (property.IsSimplex)
{
break;
}
else
{
properties = GetAssociatedProperties((IEntityComplexPropertyMetadata)property, ref ancestors);
}
}
//返回查找到的结果
return(new ReduceResult(token, property));
}
