实体框架代码首先4.3 / LINQKit相关表的谓词 [英] Entity Framework Code First 4.3 / LINQKit predicate for related table

问题描述

我正在使用具有代码优先方法的Entity Framework 4.3.1。另外，我使用LinqKit来使用PredicateBuilder。

如果我有这样的表：

位置，TimeZone（许多：1）

..我希望有这样的东西：

 表达式< Func< TimeZone，bool>> pred = PredicateBuilder.True< TimeZone>（）; 
 pred = pred.And（tz => tz.TimeZoneCode ==EST）; 
 
列表<位置> location = context.Locations 
 .AsExpandable（）。其中​​（pred）
 .Select（loc => loc）.ToList（）; 
  

这不起作用，因为谓词是构建为接受TimeZone，而是Where（）方法收到一个位置。

我可以这样重写谓词，但我不想，因为我想要一个谓词工厂，为特定类型创建谓词不想以这种方式使用导航器属性）：

 表达式< Func< Location，bool>> pred = PredicateBuilder.True< Location>（）; 
 pred = pred.And（loc => loc.TimeZone.TimeZoneCode ==EST）; 
  

我可以使用什么语法（如果有的话）使用第一个例子中构造的谓词，它需要一个TimeZone，而不是需要一个位置，并通过导航属性走树（因为这是不太可重用）。如果有一种方法可以首先利用EF对导航属性的了解，并且能够使用范围为导航属性类型的谓词。

解决方案

经过大约一个星期的努力，我发现你其实可以这样做。步骤是：

1. 定义一个谓词，它是内部属性的查询（ subPredicate ）


2. 从另一个谓词（<$）中调用 subPredicate c $ c> predicate ），反对父对象的属性。


3. 展开您的 predicate 当您在 Where 子句中使用它时。

这是您的示例的修改代码：

  var subPredicate = PredicateBuilder.True< TimeZone>（）; 
 subPredicate = subPredicate.And（tz => tz.TimeZoneCode ==EST）; 
 
 var predicate = PredicateBuilder.True< Location>（）; 
 predicate = predicate.And（l => subPredicate.Invoke（l.TimeZone））; 
 
列表<位置> locations = context.Locations 
 .AsExpandable（）。其中​​（pred.Expand（））
 .Select（loc => loc）.ToList（）; 
  

I am using Entity Framework 4.3.1 with a Code First approach. Also, I am using LinqKit so as to use the PredicateBuilder.

If I have tables like so:

Location, TimeZone (Many:1)

..and I wish to have something like so:

Expression<Func<TimeZone, bool>> pred = PredicateBuilder.True<TimeZone>();
pred = pred.And(tz => tz.TimeZoneCode == "EST");

List<Location> locations = context.Locations
    .AsExpandable().Where(pred)
    .Select(loc => loc).ToList();

This does not work, because the predicate is built to accept a TimeZone, but the Where() method receives a Location.

I can rewrite the predicate like so, but I do not want to, because I want to have a predicate factory that creates predicates for specific types (I do not want to use the Navigator properties in this manner):

Expression<Func<Location, bool>> pred = PredicateBuilder.True<Location>();
pred = pred.And(loc => loc.TimeZone.TimeZoneCode == "EST");

What syntax could I use (if any) to use the predicate as constructed in the first example, where it takes a TimeZone, rather than have it take a Location and walk the tree via the navigation properties (as this is less reusable). It would be nice if there was a way to leverage the knowledge that EF has about the navigation properties in the first place, and be able to use a predicate scoped to the type of the navigation property.

解决方案

After about a week's worth of struggling, I found out that you can in fact do this. The steps are:

1. Define a Predicate that is the query for your inner property (subPredicate)
2. Invoke that subPredicate from within another Predicate (predicate), against the property of the parent object.
3. Expand your predicate when using it in your Where clause.

Here's the revised code for your example:

var subPredicate = PredicateBuilder.True<TimeZone>();
subPredicate = subPredicate.And(tz => tz.TimeZoneCode == "EST");

var predicate = PredicateBuilder.True<Location>();
predicate = predicate.And(l => subPredicate.Invoke(l.TimeZone));

List<Location> locations = context.Locations
    .AsExpandable().Where(pred.Expand())
    .Select(loc => loc).ToList();

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