C# Linq 取得两个列表的交集

 我们经常会用到linq 来查询 一个数组中和另一个数组中相同的项， 这个时候就会用到IEqualityComparer接口。

public class StudyInfoModel

{

     public string InstanceUID = "";

}

public class StudyCompare : IEqualityComparer<StudyInfoModel>

                {

        // StudyInfoModel are equal if their UID equal.

        public bool Equals(StudyInfoModel x, StudyInfoModel y)

        {

            //Check whether the compared objects reference the same data.

            if (Object.ReferenceEquals(x, y)) return true;

            //Check whether any of the compared objects is null.

            if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))

                return false;

            //Check whether the Study' properties are equal.

            return x.InstanceUID == y.InstanceUID;

        }

        // If Equals() returns true for a pair of objects

        // then GetHashCode() must return the same value for these objects.

        public int GetHashCode(StudyInfoModel study)

        {

            //Check whether the object is null

            if (Object.ReferenceEquals(study, null)) return 0;

            //Get hash code for the Name field if it is not null.

            int hashStudyName = study.InstanceUID == null ? 0 : study.InstanceUID.GetHashCode();

            return hashStudyName;

        }

                }

以上实现了关于StudyInfoModel的IEqualityCompare接口， 其中条件为InstanceUID相同。

具体使用：

List<StudyInfoModel> StudyData = new List<StudyInfoModel>();

List<StudyInfoModel> StudyList = new List<StudyInfoModel>();

////初始化2个数组数据

.......

//取得StudyData数组中InstanceUID在StudyLIst存在的所有项

var needModifyStudy = StudyData.Intersect(StudyList, new StudyCompare()).ToList();

比如StudyData中是InstanceUID分别为1,2,3,4,5,6的数据， StudyList中是InstanceUID分别为2,4,6,8,10的数据， 

则查询结果为StudyData中2,4,6的项。