在SQL Server 2008中，TableAdapter总是为标量函数返回null

我遇到了一个奇怪的行为，我可以在一个简单的示例项目中缩小范围。

我正在尝试将相应的visual studio术语从德语翻译成英语

组件包括:- Visual Studio 2013 Express- C #—MSSQL Server 2008 R2- .NET Framework 4.5-使用DataSet和Query

示例函数非常简单:

 CREATE FUNCTION [dbo].[fTest]
    (   )
    RETURNS INT
    AS
    BEGIN
        RETURN 42
    END

然后，我使用"现有存储过程"通过TableAdapter配置助手包含了一个数据集和一个查询，使其保持默认设置。Visual Studio在上下文菜单上有一个"数据预览"功能。在那里我将收到正确的结果值。

现在添加一些简单的代码:

    using functionTest.DataSet1TableAdapters;
    using System;
    namespace functionTest
    {
        class Program
        {
            static void Main(string[] args)
            {
                QueriesTableAdapter qta = new QueriesTableAdapter();
                object result = qta.fTest();
                int? resI = (int?)result;
                Console.WriteLine("result: " + resI);
            }
        }
    }

奇怪的是结果总是null

编辑:

生成的TableAdapter代码:

namespace functionTest.DataSet1TableAdapters {

    /// <summary>
    ///Represents the connection and commands used to retrieve and save data.
    ///</summary>
    [global::System.ComponentModel.DesignerCategoryAttribute("code")]
    [global::System.ComponentModel.ToolboxItem(true)]
    [global::System.ComponentModel.DataObjectAttribute(true)]
    [global::System.ComponentModel.DesignerAttribute("Microsoft.VSDesigner.DataSource.Design.TableAdapterDesigner, Microsoft.VSDesigner" +
        ", Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
    [global::System.ComponentModel.Design.HelpKeywordAttribute("vs.data.TableAdapter")]
    public partial class QueriesTableAdapter : global::System.ComponentModel.Component {
        private global::System.Data.IDbCommand[] _commandCollection;
        [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]
        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("System.Data.Design.TypedDataSetGenerator", "4.0.0.0")]
        protected global::System.Data.IDbCommand[] CommandCollection {
            get {
                if ((this._commandCollection == null)) {
                    this.InitCommandCollection();
                }
                return this._commandCollection;
            }
        }
        [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]
        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("System.Data.Design.TypedDataSetGenerator", "4.0.0.0")]
        private void InitCommandCollection() {
            this._commandCollection = new global::System.Data.IDbCommand[1];
            this._commandCollection[0] = new global::System.Data.SqlClient.SqlCommand();
            ((global::System.Data.SqlClient.SqlCommand)(this._commandCollection[0])).Connection = new global::System.Data.SqlClient.SqlConnection(global::functionTest.Properties.Settings.Default.connectionString);
            ((global::System.Data.SqlClient.SqlCommand)(this._commandCollection[0])).CommandText = "dbo.fTest";
            ((global::System.Data.SqlClient.SqlCommand)(this._commandCollection[0])).CommandType = global::System.Data.CommandType.StoredProcedure;
            ((global::System.Data.SqlClient.SqlCommand)(this._commandCollection[0])).Parameters.Add(new global::System.Data.SqlClient.SqlParameter("@RETURN_VALUE", global::System.Data.SqlDbType.Int, 4, global::System.Data.ParameterDirection.ReturnValue, 10, 0, null, global::System.Data.DataRowVersion.Current, false, null, "", "", ""));
        }
        [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]
        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("System.Data.Design.TypedDataSetGenerator", "4.0.0.0")]
        [global::System.ComponentModel.Design.HelpKeywordAttribute("vs.data.TableAdapter")]
        public virtual object fTest() {
            global::System.Data.SqlClient.SqlCommand command = ((global::System.Data.SqlClient.SqlCommand)(this.CommandCollection[0]));
            global::System.Data.ConnectionState previousConnectionState = command.Connection.State;
            if (((command.Connection.State & global::System.Data.ConnectionState.Open) 
                        != global::System.Data.ConnectionState.Open)) {
                command.Connection.Open();
            }
            object returnValue;
            try {
                returnValue = command.ExecuteScalar();
            }
            finally {
                if ((previousConnectionState == global::System.Data.ConnectionState.Closed)) {
                    command.Connection.Close();
                }
            }
            if (((returnValue == null) 
                        || (returnValue.GetType() == typeof(global::System.DBNull)))) {
                return null;
            }
            else {
                return ((object)(returnValue));
            }
        }
    }
}

编辑:

另一个提示:内部CommandCollection包含有效的结果。我在调试器中验证了这一点，也通过暴露CommandCollection并访问它:

IDataParameterCollection test = qta._commandCollection[0].Parameters;
SqlParameter param = (SqlParameter) test[0];
int? res = (int?) param.Value;

returnValue = command.ExecuteScalar();

command.ExecuteScalar();
returnValue = command.Parameters["@RETURN_VALUE"].Value;