Question

var query = (from objectType in _session.GetAll<ObjectType>()
  let currentVersion = objectType
      .ObjectTypeVersions.OrderByDescending(x =>x.ObjectTypeVersionId)
      .FirstOrDefault()
  where 
      objectType.Active && 
      currentVersion.Active && 
      objectType.ContentTemplate.Active
  select currentVersion);

我有这样的查询，我不明白它的作用。我想用方法语法重写它。

Answer 1

查询语法只是语法糖。您可以使用反编译器（如ILSpy）转换为扩展方法表示法。经过一些清理后，我得到的是：

var query = objectTypes.Select(objectType => new
{
    objectType = objectType, 
    currentVersion = objectType.ObjectTypeVersions
        .OrderByDescending(x => x.ObjectTypeVersionId).FirstOrDefault()
}).Where(x => x.objectType.Active && x.currentVersion.Active && 
    x.objectType.ContentTemplate.Active).Select(x => x.currentVersion);

作为参考，这是ILSpy生成的原始代码......基本上是相同的，但生成的变量名称不是有效的C＃标识符，并且不必要地显式输入。

IEnumerable<ObjectTypeVersion> query = objectTypes.Select((ObjectType objectType) => new
{
    objectType = objectType,
    currentVersion = objectType.ObjectTypeVersions.OrderByDescending((ObjectTypeVersion x) => x.ObjectTypeVersionId).FirstOrDefault<ObjectTypeVersion>()
}).Where(<>h__TransparentIdentifier0 => <>h__TransparentIdentifier0.objectType.Active && <>h__TransparentIdentifier0.currentVersion.Active && <>h__TransparentIdentifier0.objectType.ContentTemplate.Active).Select(<>h__TransparentIdentifier0 => <>h__TransparentIdentifier0.currentVersion);

Answer 2

我肯定会使用查询语法。但这里是lambda语法：

var query = _session.GetAll<ObjectType>()
     .Select(objectType => new {
          objectType,
          currentVersion = objectType.ObjectTypeVersions.OrderByDescending(otv => otv.ObjectTypeVersionId).FirstOrDefault()
      }).Where(x => x.objectType.Active && x.currentVersion.Active && x.objectType.ContentTemplate.Active)
        .Select(x => x.currentVersion);

这里的主要想法是创建匿名类型，其中包含objectType关键字引入的原始查询变量currenVersion和第二个let。

请帮我简化并转换为点符号linq查询

2 个答案: