Question

可能重复：
How can I send where statements to a method which are dynamically executed in a LINQ statement?

我一直在用不同的方法编写简单的LINQ查询，但它们已经变得重复了。请原谅名称和地点的愚蠢示例，所有三种方法中唯一改变的部分是'where'子句。

如何使这个重复的代码更加dry？

例如，类似于辅助方法的方法，它将所有内容都相同但允许更改where子句。

public IEnumerable<NamePlace> GetSomeData(int num1, int num2)
{
  var temp = from Name in Names
             from Place in Places
             where Name.id == num1 && Place.id = num2
             select new NamePlace {
                  field1 = Name.name;
                  field2 = Place.name;
             };
  return temp;
}

public IEnumerable<NamePlace> GetSomeData2(int num1, int num2)
{
  var temp = from Name in Names
             from Place in Places
             where Name.age == num1 && Place.streetNumber = num2
             select new NamePlace {
                  field1 = Name.name;
                  field2 = Place.name;
             };
  return temp;
}

public IEnumerable<NamePlace> GetSomeData3(int num1, int num2)
{
  var temp = from Name in Names
             from Place in Places
             where Name.favouriteNumber == num1 && Place.neighbourNumber = num2
             select new NamePlace {
                  field1 = Name.name;
                  field2 = Place.name;
             };
  return temp;
}

Answer 1

您需要的只是Func<T1, T2, bool>类型的参数，其中T1和T2分别是Names和Places中的项目类型。

private IEnumerable<NamePlace> GetSomeDataHelper(Func<Name, Place, bool> filter)
{
  var query = from name in Names
             from place in Places
             where filter(name, place)
             select new NamePlace {
                  field1 = name.name,
                  field2 = place.name,
             };
  return query;
}

public IEnumerable<NamePlace> GetSomeData1(int num1, int num2)
{
    return GetSomeDataHelper((name, place) => name.id == num1 && place.id = num2);
}

Answer 2

将Func<Name, Place,bool>传递给方法，在Where子句中对其进行评估。

public IEnumerable<NamePlace> GetSomeData(Func<Name,Place, bool> condition)
{
  var temp = from Name in Names
             from Place in Places
             where condition(Name,Place)
             select new NamePlace {
                  field1 = Name.name;
                  field2 = Place.name;
             };
  return temp;
}

然后调用这样的函数：

GetSomeData((name,place)=>name.FavNumber=5 && Place.Neighbor==7);

Answer 3

你可以这样做，GetSomeData（）接受谓词：

public IEnumerable<NamePlace> GetSomeData(int num1, int num2, Func<Name, Place, bool> predicate)
{
    var temp = from Name in Names
         from Place in Places
         where predicate(Name, Place)
         select new NamePlace {
              field1 = Name.name;
              field2 = Place.name;
         };
   return temp;
}

然后你可以这样称呼它：

var results = GetSomeData(num1, num2, (name, place) => name.id == num1 && place.id = num2);

减少类似查询中的重复

3 个答案: