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转换错误为int? 在实体框架中字符串

[英]Conversion error int? to string in Entity Framework

I have problems trying to left join in a table where the PK and FK has different types. 我在尝试在PK和FK具有不同类型的表中保留联接时遇到问题。 int? 诠释? to string, decimal to string and vice-versa 到字符串,十进制到字符串,反之亦然

public VDB_TABLE1()
{
   public int Id {get; set;}
   public string AnotherValue {get; set;}
   public string FKTable2 {get; set;}
   public string FKTable3 {get; set;}
}

public VDB_TABLE2()
{
   public int? PKTable2 {get; set;}
   public string AnotherValue {get; set;}
}

public VDB_TABLE3()
{
   public decimal PKTable3 {get; set;}
   public string AnotherValue {get; set;}
}

That's my ViewModel: 那就是我的ViewModel:

public VDB_MYVIEWMODEL()
{
   public int Id {get; set;}
   public string AnotherValue {get; set;}
   public VDB_TABLE2 TABLE2 {get; set;}
   public VDB_TABLE3 TABLE3 {get; set;}
}

The query: 查询:

 var query = (from t1 in context.VDB_TABLE1
                from t2 in context.VDB_TABLE2.Where(t2 => t2.PKTable2 == t1.FKTable2).DefaultIfEmpty()
                from t3 in context.VDB_TABLE3.Where(t3 => t3.PKTable3 == t1.FKTable3).DefaultIfEmpty()
 select new MYVIEWMODEL
 {
   Id = t1.Id,
   AnotherValue = t1.AnotherValue,
   TABLE2 = t2,
   TABLE3 = t3
 }).ToList();

It may be impossible to get EF to behave this way. EF可能无法以这种方式运行。 MSSQL Server will not even let you make this type of relationship. MSSQL Server甚至不允许您建立这种类型的关系。 If you don't mind a little SQL, you can do what you want using LinqToSQL 如果您不介意使用SQL,可以使用LinqToSQL做您想做的事

Modify your view model 修改您的视图模型

public VDB_MYVIEWMODEL()
{
   public int Id {get; set;}
   public string AnotherValue {get; set;}
   public string T2 {get; set;}
   public string T3 {get; set;}
}

string sSQL "Select VDB_TABLE1.Id, VDB_TABLE1.AnotherValue, VDB_TABLE2.AnotherValue as T2, VDB_TABLE3.AnotherValue as T3 from VDB_TABLE1 left join VDB_TABLE2 on VDB_TABLE1.FKTable2 = VDB_TABLE2.PKTable2 left join VDB_TABLE3 on VDB_TABLE1.FKTable3 = VDB_TABLE3.PKTable3;";

List<VDB_MYVIEWMODEL> Results = context.Database.SqlQuery<VDB_MYVIEWMODEL>(sSql).ToList();

One other option would be to change your model like so. 另一种选择是像这样更改您的模型。

public VDB_TABLE1()
{
   public int Id {get; set;}
   public string AnotherValue {get; set;}
   public string FKTable2 {get; set;}
   public VDB_TABLE2 Table2
   {
     get
     {
       int id = Convert.ToInt32(FKTable2);
       return context.VDB_TABLE2.Find(id);
     }
   }

   ...do similar for Table3
}

Query like so, and access the values like: 像这样查询,并访问类似的值:

var query = (from t1 in context.VDB_TABLE1);

query.Id
query.AnotherValue
query.Table2.AnotherValue
query.Table3.AnotherValue

Warning, this is very inefficient. 警告,这是非常低效的。 You are making two extra db calls for every record in your primary table. 您正在对主表中的每个记录进行两个额外的数据库调用。 If you only have a few records...then this might be OK for you. 如果您只有几条记录...那么这对您来说可能就可以了。

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