实体框架-选择有无关系

问题描述

如果我有一组表，TableA，TableB，TableC和TableD，而TableA与TableB，TableC和TableD具有一对多的关系.

If I have a set of tables, TableA, TableB, TableC and TableD with TableA having one to many relationships with TableB, TableC and TableD.

有时我想返回整个TableA，TableB，TableC和TableD集.有时我只想返回TableA.

Sometimes I want to return the entire set of TableA, TableB, TableC and TableD. Sometimes I want to return just TableA.

目前，我有以下内容:

TableA tableA;

if (includeRelationships)
{
    tableA = (from a in context.TableAs
                   .Include("TableBs")
                   .Include("TableCs")
                   .Include("TableDs")
              where a.Id = myId
              select a).SingleOrDefault();
}
else
{
    tableA = (from a in context.TableAs
              where a.Id = myId
              select a).SingleOrDefault();
}

// do stuff with tableA

这是唯一的方法吗?

编辑-根据feanz的回答进行澄清:

这将作为WCF服务公开，因此它必须是单个DB调用(所有表或单个TableA)，因此不能选择延迟/延迟加载.

This will be exposed as a WCF service so it needs to be a single DB call, either all tables or single TableA, so Lazy / Deferred Loading is not an option.

推荐答案

执行类似的操作

var query = context.TableA;
if (includeRelationships) 
{
   query = query.Include("Tableb").Include("TableC").Include("TableD");
}
var tablea = query.SingleOrDefault();

在这种情况下，您使用的是扩展方法"Include"采用并返回IQueryable的事实.您可能要使用:

In this case you are using the fact that the extension method "Include" takes and returns an IQueryable. You might want to use the:

query.Include(x => x.TableB)...

以表达式为参数的方法的重载.这样，编译器将为您进行检查.如果您使用的是EF的较旧版本，则可能无法访问它.

overload of the method that takes an expression as a parameter. That way the compiler will do the checking for you. You may not have access to it if you are using an older version of EF.

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