实体框架-如何在没有LINQ和只有字符串的情况下连接表？

Question

我有一个关于实体框架的问题。如果你知道答案，请回答。我有这样的疑问：

String queryRaw =
    "SELECT " +
    "p.ProductName AS ProductName " +
    "FROM ProductEntities.Products AS p " +
    "INNER JOIN CategoryEntities.Categories AS c " + 
    "ON p.CategoryID = c.CategoryID ";

ObjectQuery<DbDataRecord> query = new ObjectQuery<DbDataRecord>(queryRaw, entityContext);

GridView1.DataSource = query;
GridView1.DataBind();

特别是，我想在一个查询中加入几个表，但是我不能使用LINQ，也不能在查询中使用映射到DB字段的对象的ObjectQuery。因为每个实体都是动态创建的。所以这是我不能用的：

msdn.microsoft.com/en-us/library/bb425822.aspx#linqtosql_topic12

msdn.microsoft.com/en-us/library/bb896339%28v=VS.90%29.aspx

问题是，我能用这样的东西代替对象吗？

query.Join ("INNER JOIN CategoryEntities.Category ON p.CategoryID = c.CategoryID ");

目的是使用ObjectQuery的联接方法和语法，如Where方法:

msdn.microsoft.com/en-us/library/bb338811%28v=VS.90%29.aspx

谢谢你，阿特姆

Answer 1

最后我找到了一个更好的解决方案，我们可以使用Sub查询内部的主查询。例如：

var db = CustomEntity();

ObjectQuery<Categories> query1 = db.Categories.Where("it.CategoryName='Demo'").Select ("it.CategoryID");
var categorySQL = query1.ToTraceString().Replace("dbo", "CustomEntity"); // E-SQL need this syntax
ObjectQuery<Products> query2 = db.Categories.Where("it.CategoryID = (" + categorySQL + ")");

以下是一些例子：

http://msdn.microsoft.com/en-us/library/bb896238.aspx

祝好运!

Answer 2

我现在看到的任何决定都是将ObjectQuery临时转换为string，将联合表添加为string，然后将其转换回ObjectQuery：

RoutesEntities routesModel = new RoutesEntities(entityConnection);
String queryRaw = "SELECT " + 
                  "rs.RouteID AS RouteID, " +
                  "rs.LocaleID AS LocaleID, " + 
                  "rs.IsSystem AS IsSystem " +
                  "FROM RoutesEntities.Routes AS rs ";

_queryData = new ObjectQuery<DbDataRecord>(queryRaw, routesModel);

var queryJoin = _queryData.CommandText + " INNER JOIN LocalesEntities.Locales AS ls ON ls.LocaleID = rs.LocaleID ";
_queryData = new ObjectQuery<DbDataRecord>(queryJoin, routesModel);

也许有人有更一致的建议？