LINQ的Distinct總結

LINQ命名空間下的Distinct方法有兩個重載，一個是對TSource的Queryable可查詢結果集支援的，别一個是隻對Ｔ的IList,Enumerable結果集支援的

看一下，如果是傳回為iqueryable<T>結果集，隻能用distinct()預設的方法，

如果是List<T>，就可以根據自己定義好的比較原則，進行字段級的過濾了

例如，可以對Person類，進行ＩＤ，與Name的相等來确實整個對象是否與其它執行個體對象相等：

 public class Person

    {

        public int ID { get; set; }

        public string Name { get; set; }

        public string Email { get; set; }

    }

    public class PersonCompar : System.Collections.Generic.IEqualityComparer<Person>

        public bool Equals(Person x, Person y)

        {

            if (x == null)

                return y == null;

            return x.ID == y.ID;

        }

        public int GetHashCode(Person obj)

            if (obj == null)

                return 0;

            return obj.ID.GetHashCode();

如果一個list<person>的執行個體為

personList，那麼，它根據ＩＤ過濾的程式為

 personList.Distinct(new PropertyComparer<Person>("ID")).ToList().ForEach(i => Console.WriteLine(i.ID + i.Name));

PropertyComparer.cs代碼如下

 /// <summary>

    /// 屬性比較器

    /// </summary>

    /// <typeparam name="T"></typeparam>

    public class PropertyComparer<T> : IEqualityComparer<T>

        private PropertyInfo _PropertyInfo;

        /// <summary>

        /// 通過propertyName 擷取PropertyInfo對象        /// </summary>

        /// <param name="propertyName"></param>

        public PropertyComparer(string propertyName)

            _PropertyInfo = typeof(T).GetProperty(propertyName,

            BindingFlags.GetProperty | BindingFlags.Instance | BindingFlags.Public);

            if (_PropertyInfo == null)

            {

                throw new ArgumentException(string.Format("{0} is not a property of type {1}.",

                    propertyName, typeof(T)));

            }

        #region IEqualityComparer<T> Members

        public bool Equals(T x, T y)

            object xValue = _PropertyInfo.GetValue(x, null);

            object yValue = _PropertyInfo.GetValue(y, null);

            if (xValue == null)

                return yValue == null;

            return xValue.Equals(yValue);

        public int GetHashCode(T obj)

            object propertyValue = _PropertyInfo.GetValue(obj, null);

            if (propertyValue == null)

            else

                return propertyValue.GetHashCode();

        #endregion