减少类似查询中的重复

Question

可能的重复项：
如何将 where 语句发送到在 LINQ 语句中动态执行的方法？

我一直在单独的方法中编写简单的 LINQ 查询，但它们变得重复。请原谅名称和地点的愚蠢示例，所有三种方法中唯一更改的部分是"where"子句。

如何使这种重复的代码更加枯燥？

例如，类似于帮助程序的方法，它采用相同的所有内容，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

只需要一个类型为 Func<T1, T2, bool> 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>传递给该方法，在 Where 子句中对其进行计算。

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;
}

然后像这样调用函数：

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

Answer 3

你可以

让它让GetSomeData（）接受一个谓词：

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);