我怎样才能确定是否

Question

我正在写一个代码生成和我被陷在确定一个存储过程的结果集列的可空状态的存储过程结果的列可以为空。我可以查询的数据类型就好了，但无论是DataReader对象，也不是数据表列包含我的专栏的正确空值。

 public List<DataColumn> GetColumnInfoFromStoredProcResult(string schema, string storedProcName) 
    { 
     //build sql text 
     var sb = new StringBuilder(); 
     sb.Append("SET FMTONLY OFF; SET FMTONLY ON; \n");//this is how EF4.1 did so I copied..not sure why the repeat 

     sb.Append(String.Format("exec {0}.{1} ", schema, storedProcName)); 

     var prms = GetStoredProcedureParameters(schema: schema, sprocName: storedProcName); 
     var count = 1; 
     foreach (var param in prms) 
     { 
      sb.Append(String.Format("{0}=null", param.Name)); 
      if (count < prms.Count) 
      { 
       sb.Append(", "); 
      } 
      count++; 
     } 

     sb.Append("\n SET FMTONLY OFF; SET FMTONLY OFF;"); 

     var dataTable = new DataTable(); 
     //var list = new List<DataColumn>(); 

     using (var sqlConnection = this.SqlConnection) 
     { 
      using (var sqlAdapter = new SqlDataAdapter(sb.ToString(), sqlConnection)) 
      { 
       if (sqlConnection.State != ConnectionState.Open) sqlConnection.Open(); 
       sqlAdapter.SelectCommand.ExecuteReader(CommandBehavior.KeyInfo); 
       sqlConnection.Close(); 
       sqlAdapter.Fill(dataTable); 
      } 

      //using (var sqlCommand = new SqlCommand()) 
      //{ 

      // sqlCommand.CommandText = sb.ToString(); 
      // sqlCommand.CommandType = CommandType.Text; 
      // sqlCommand.Connection = sqlConnection; 
      // if (sqlConnection.State != ConnectionState.Open) sqlConnection.Open(); 

      // var dr = sqlCommand.ExecuteReader(CommandBehavior.SchemaOnly); 
      // var whateva = dr.GetSchemaTable(); 

      // foreach (DataColumn col in whateva.Columns) 
      // { 
      //  list.Add(col); 
      // } 
      //} 
     } 

     var list = dataTable.Columns.Cast<DataColumn>().ToList(); 

     return list; 
    } 

我试图从一个存储过程类似于在实体框架创建一个复杂类型的东西结束。我可以劫持该功能吗？

在这个例子中，ID列.. tblJobId（不是我个人的称呼）将不能为空。但我选择null作为ImNull，它具有所有的相同属性那么，如何EF确定相应的C＃数据类型应可以为空还是不可以？

有没有人做过这个..

想法是赞赏。

Answer 1

秘密是使用Schema Only并填充数据集不可数据表。现在，datacolumn上的AllowDbNull属性正确显示返回值的可空状态。

这是它...

public List<DataColumn> GetColumnInfoFromStoredProcResult(string schema, string storedProcName) 
    { 
     //build sql text 
     var sb = new StringBuilder(); 
     sb.Append("SET FMTONLY OFF; SET FMTONLY ON; \n");//this is how EF4.1 did so I copied..not sure why the repeat 

     sb.Append(String.Format("exec {0}.{1} ", schema, storedProcName)); 

     var prms = GetStoredProcedureParameters(schema: schema, sprocName: storedProcName); 
     var count = 1; 
     foreach (var param in prms) 
     { 
      sb.Append(String.Format("{0}=null", param.Name)); 
      if (count < prms.Count) 
      { 
       sb.Append(", "); 
      } 
      count++; 
     } 

     sb.Append("\n SET FMTONLY OFF; SET FMTONLY OFF;"); 

     var ds = new DataSet(); 
     using (var sqlConnection = this.SqlConnection) 
     { 
      using (var sqlAdapter = new SqlDataAdapter(sb.ToString(), sqlConnection)) 
      { 
       if (sqlConnection.State != ConnectionState.Open) sqlConnection.Open(); 
       sqlAdapter.SelectCommand.ExecuteReader(CommandBehavior.SchemaOnly); 
       sqlConnection.Close(); 
       sqlAdapter.FillSchema(ds, SchemaType.Source, "MyTable"); 
      } 
     } 

     var list = ds.Tables[0].Columns.Cast<DataColumn>().ToList(); 

     return list; 
    } 

    public List<SqlParamInfo> GetStoredProcedureParameters(string schema, string sprocName) 
    { 
     var sqlText = String.Format(
      @"SELECT 
       [Name] = N'@RETURN_VALUE', 
       [ID] = 0, 
       [Direction] = 6, 
       [UserType] = NULL, 
       [SystemType] = N'int', 
       [Size] = 4, 
       [Precision] = 10, 
       [Scale] = 0 
      WHERE 
       OBJECTPROPERTY(OBJECT_ID(N'{0}.{1}'), 'IsProcedure') = 1 
      UNION 
      SELECT 
       [Name] = CASE WHEN p.name <> '' THEN p.name ELSE '@RETURN_VALUE' END, 
       [ID] = p.parameter_id, 
       [Direction] = CASE WHEN p.is_output = 0 THEN 1 WHEN p.parameter_id > 0 AND p.is_output = 1 THEN 3 ELSE 6 END, 
       [UserType] = CASE WHEN ut.is_assembly_type = 1 THEN SCHEMA_NAME(ut.schema_id) + '.' + ut.name ELSE NULL END, 
       [SystemType] = CASE WHEN ut.is_assembly_type = 0 AND ut.user_type_id = ut.system_type_id THEN ut.name WHEN ut.is_user_defined = 1 OR ut.is_assembly_type = 0 THEN st.name WHEN ut.is_table_type =1 Then 'STRUCTURED' ELSE 'UDT' END, 
       [Size] = CONVERT(int, CASE WHEN st.name IN (N'text', N'ntext', N'image') AND p.max_length = 16 THEN -1 WHEN st.name IN (N'nchar', N'nvarchar', N'sysname') AND p.max_length >= 0 THEN p.max_length/2 ELSE p.max_length END), 
       [Precision] = p.precision, 
       [Scale] = p.scale 
      FROM 
       sys.all_parameters p 
       INNER JOIN sys.types ut ON p.user_type_id = ut.user_type_id 
       LEFT OUTER JOIN sys.types st ON ut.system_type_id = st.user_type_id AND ut.system_type_id = st.system_type_id 
      WHERE 
       object_id = OBJECT_ID(N'{0}.{1}') 
      ORDER BY 2", schema, sprocName); 


     using (var sqlConnection = this.SqlConnection) 
     { 
      using (var sqlCommand = new SqlCommand()) 
      { 
       if (sqlConnection.State != ConnectionState.Open) sqlConnection.Open(); 

       sqlCommand.Connection = sqlConnection; 
       sqlCommand.CommandType = CommandType.Text; 
       sqlCommand.CommandText = sqlText; 

       var dr = sqlCommand.ExecuteReader(); 

       var result = new List<SqlParamInfo>(); 

       while (dr.Read()) 
       { 
        if (Convert.ToString(dr["Name"]) != "@RETURN_VALUE") 
        { 
         result.Add(new SqlParamInfo(dr)); 
        } 
       } 

       return result; 
      } 
     } 
    } 

Answer 2

假设，每一个这来自SP柱可以为空 - 这是因为存储过程的一个有效的假设 - 其一种数据抽象层，因此，其代码可以改变的，但仍然产生有效结果。

如果列是不可为空昨天没什么意思了今天。所以 - 来自SP结果集的所有列都可以通过设计来空。

更新。

假设表T1具有列Id INT IDENTITY PRIMARY KEY

你的存储过程是这样的：

CREATE PROC p1 
AS 
BEGIN 
    SELECT Id FROM t1 
END 

所以它永远不会返回一个id = NULL，但这是SP - 数据的抽象，所以 - 明天我将修改它是这样的：

CREATE PROC p1 
AS 
BEGIN 
    SELECT Id FROM t1 
    UNION 
    SELECT NULL 
END 

所以，现在返回NULL - 想一想。理解数据抽象的差异