C# Linq 查询返回 true 或 false

Linq query return true or false

提问by Indhi

I have a query where it should return TRUE or FALSE.

我有一个查询，它应该返回 TRUE 还是 FALSE。

var query = from c in db.Emp
            from d in db.EmpDetails 
            where c.ID == d.ID && c.FirstName == "A" && c.LastName == "D" 
          // It should return TRUE when this above statement matches all these conditions

and I want to attach this query result to a property(of string datatype)

我想将此查询结果附加到属性（字符串数据类型）

this.result = Conert.ToBoolean(query);

how to achieve this in LINQ ?

如何在 LINQ 中实现这一点？

EDIT:

编辑：

EmpMapper class

EmpMapper 类

  public class EmpMapper
  {
    EmpEntities db;
    // ID column already exists in the DB
    private int ID;
    // I am creating this property to add it from the UI side, depending on the certain conditions in the query. That is why I created a separate class to map the existing ID from the DB
    bool result;
    public EmpMapper(int ID, bool result)
    {
      this.db = new EmpEntites();
      this.ID = ID;
      var query = from c in db.Emp
            from d in db.EmpDetails 
            where c.ID == d.ID && c.FirstName == "A" && c.LastName == "D" 
          // It should return TRUE when this above statement matches all these conditions
      this.result = Convert.ToBoolean(query);
    }
   public int ID
   {
    get{return this.ID;}
    set{this.ID = value;}
   }
   public bool result
   {
    get{return this.result;}
    set{this.result = value;}
   }
   } 

MainViewModel class

MainViewModel 类

      List<EmpMapper> empMapCol = new List<EmpMapper>();

     private void Page_Loaded(object sender, RoutedEventArgs e)
    {
      var emp_query = from c in db.Emp
                      orderby c.ID
                      select a;
     List<Emp> empCol = emp_query.ToList();
     foreach(Emp item in empCol)
     {
       this.empMapCol.Add(new EmpMapper(item.ID, item.result)); 
     }
     datagrid1.ItemsSource = empMapCol;
     }
     }

采纳答案by Satpal

try this,

尝试这个，

 var query = (from c in db.Emp
        from d in db.EmpDetails 
        where c.ID == d.ID && c.FirstName == "A" && c.LastName == "D"
         select c 
         ).Any(); 

  this.result = query; //no need to convert to boolean its already bool value

回答by Skinny Pipes

var query = from c in db.Emp
            from d in db.EmpDetails 
            select new { c.ID == y.ID &&  
                         c.FirstName == "A" && 
                         c.LastName == "D" };

回答by Oscar Foley

You can use .Any() or .Count(). Any()is performing better. (Check this SO questionto see why)

您可以使用 .Any() 或 .Count()。Any()表现更好。（检查这个SO 问题以了解原因）

.Any()

。任何（）

var query = from c in db.Emp
            from d in db.EmpDetails 
            where c.ID == d.ID && c.FirstName == "A" && c.LastName == "D" 
          // It should return TRUE when this above statement matches all these conditions
this.result = query.Any().ToString()

.Count()

。数数（）

var query = from c in db.Emp
            from d in db.EmpDetails 
            where c.ID == d.ID && c.FirstName == "A" && c.LastName == "D" 
          // It should return TRUE when this above statement matches all these conditions
this.result = (query.Count() > 0).ToString()

回答by Maciej

If I understand you correctly you want to get trueif one of the results of the query matches all conditions. In that case try something like this:

如果我理解正确，您希望获得true查询结果之一是否与所有条件匹配。在这种情况下，请尝试以下操作：

var found =
    (from c in db.Emp
    from d in db.EmpDetails
    where c.ID == y.ID && c.FirstName == "A" && c.LastName == "D"
    select c).Any();

this.result = found.ToString();

回答by user2141886

If you really want to have a "true" or "false" String Response:

如果你真的想要一个“真”或“假”的字符串响应：

    public string result
    {
        get
        {
            return db.Emp.SelectMany(c => db.EmpDetails, (c, d) => new {c, d})
                         .Where(@t => c.ID == y.ID && c.FirstName == "A" && c.LastName == "D")
                         .Select(@t => c)).Any().ToString();
        }
    }

But I would suggest to make the property "result" a bool and remove the ToString(). Once you have a bool you can always do a ToString() on it

但我建议将属性“result”设为 bool 并删除 ToString()。一旦你有一个 bool 你就可以在它上面做一个 ToString()