Question

所以我的问题是这个。当使用Data Context ExecuteQuery（字符串查询，params object []参数）（here）时，我无法以任何形式或形式传递null。启动此操作的参数是SQL nvarchar参数，需要允许空值。

我在stackoverflow上读到这个article，其中“使用DBNull.Value”标记为答案 - 所以我尝试了，没有任何东西（如果它不起作用，那么想知道答案是怎么回事？？！）。

以下是我尝试运行的示例代码（注意，这只是为了测试这个概念）：

var db = new Test1DataContext(Properties.Settings.Default.TestConnectionString);
var query = "EXEC UpInsertTest4 {0}, {1}";

// Works fine
var list1 = new List<object> { 1, "1" };
db.ExecuteQuery<UpInsertTest4Result>(query, list1.ToArray());

// Doesn't work
var list2 = new List<object> { 1, DBNull.Value };
db.ExecuteQuery<UpInsertTest4Result>(query, list2.ToArray());

以下是我收到的各种错误：

null                : A query parameter cannot be of type 'System.Object'.
default(string)     : A query parameter cannot be of type 'System.Object'.
DBNull.Value        : Unexpected type code: DBNull (which give this as a stack trrace)


at System.Data.Linq.SqlClient.SqlTypeSystem.Sql2005Provider.From(Type type, Nullable`1 size)
   at System.Data.Linq.SqlClient.SqlTypeSystem.Sql2008Provider.From(Type type, Nullable`1 size)
   at System.Data.Linq.SqlClient.SqlTypeSystem.ProviderBase.From(Type type)
   at System.Data.Linq.SqlClient.SqlTypeSystem.ProviderBase.From(Object o)
   at System.Data.Linq.SqlClient.SqlFactory.ValueFromObject(Object value, Type clrType, Boolean isClientSpecified, Expression sourceExpression)
   at System.Data.Linq.SqlClient.QueryConverter.VisitConstant(ConstantExpression cons)
   at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp)
   at System.Data.Linq.SqlClient.QueryConverter.VisitUserQuery(String query, Expression[] arguments, Type resultType)
   at System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc)
   at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.ConvertOuter(Expression node)
   at System.Data.Linq.SqlClient.SqlProvider.BuildQuery(Expression query, SqlNodeAnnotations annotations)
   at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
   at System.Data.Linq.DataContext.ExecuteMethodCall(Object instance, MethodInfo methodInfo, Object[] parameters)
   at System.Data.Linq.DataContext.ExecuteQuery[TResult](String query, Object[] parameters)
   at ConsoleApplication1.Program.Main(String[] args) in E:\TestBed\Testbed\ConsoleApplication1\Program.cs:line 36
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

从我读过的内容来看，我可能正在为此而战！这是我最后的尝试！

非常感谢，
克里斯。

Answer 1

你可以这样做：

db.ExecuteQuery<UpInsertTest4Result>(string.Format(query,1,"null"));

<强>更新

是的，我已经测试了解决方案。它不会包含@p1=N'null'。因为我直接使用sql作为字符串。所以概念很多。

存储程序：

CREATE PROCEDURE testas
@test1 INT,  
@test2 INT 
AS
SELECT 1 test

用于测试输出的类：

public class testout
{
    public int test { get; set; }
}

使用db上下文查询Linq：

var query="exec testas {0}, {1}";
db.ExecuteQuery<testout>(string.Format(query,"0","null"));

如果你查看linqpad，sql输出是这样的：

exec testas 0, null

字符串格式正在改变字符串。这与写这个相同：

db.ExecuteQuery<testout>("exec testas 0, null")

Answer 2

我遇到了同样的问题，我在这个论坛上找到了解决方案：https://social.msdn.microsoft.com/Forums/en-US/20b318bc-32cf-466b-972e-6cd37e625cd6/a-query-parameter-cannot-be-of-the-type-systemobject?forum=linqprojectgeneral

基本上，目标是创建一个扩展方法，该方法将分析参数并将所有空参数直接替换为请求示例：＆＃34; EXEC MyStoredProcedure {0}，{1}，{2}，{3}＆＃34;第二个参数值为null将变为＆＃34; EXEC MyStoredProcedure {0}，NULL，{1}，{2}＆＃34;第二个参数将从数组参数中删除。

以下是方法：

internal static IEnumerable<TResult> ExecuteQueryNullSafe<TResult>(this System.Data.Linq.DataContext context, string command, params object[] parameters)
{
  var list = new List<object>();
  var listVals = new List<bool>();

  for (int x = 0; x < parameters.Count(); x++)
  {
    if (parameters[x] == null || parameters[x] is System.DBNull)
    {
      command = command.Replace("{" + x + "}", "NULL");
      listVals.Add(false);
    }
    else
    {
      list.Add(parameters[x]);
      listVals.Add(true);
    }
  }

  int nextId = 0;
  for (int i = 0; i < listVals.Count; i++)
  {
    var isUsed = listVals[i];
    if (!isUsed)
      continue;
    if (nextId != i)
      command = command.Replace("{" + i.ToString() + "}", "{" + nextId.ToString() + "}");
    nextId++;
  }

  return context.ExecuteQuery<TResult>(command, list.ToArray());
}

Answer 3

试试这个克里斯：

void Main()
{
    var db = new Test1DataContext(Properties.Settings.Default.TestConnectionString);
    db.UpInsertTest4Result(1,"1");
    db.UpInsertTest4Result(1,null);
    db.UpInsertTest4Result(null,"1");
    db.UpInsertTest4Result(null,null);
}

public class Test1DataContext : DataContext
{
   public Test1DataContext(string connStr) : base(connStr) { }

   [Function(Name = "UpInsertTest4")]
   public IEnumerable<UpInsertTest4Result> UpInsertTest4Result(
    [Parameter(Name = "par1", DbType = "Int")] int? par1,
    [Parameter(Name = "par2", DbType = "VarChar")] string par2)
   {
       var result = this.ExecuteMethodCall(this, ((MethodInfo)(MethodInfo.GetCurrentMethod())), par1,par2);

       return (IEnumerable<UpInsertTest4Result>)result.ReturnValue;
   }
}

DataContext.ExecuteQuery <tentity>和Null值</tentity>

3 个答案: