LINQ的Distinct总结

LINQ命名空间下的Distinct方法有两个重载，一个是对TSource的Queryable可查询结果集支持的，别一个是只对Ｔ的IList,Enumerable结果集支持的

看一下，如果是返回为iqueryable<T>结果集，只能用distinct()默认的方法，

如果是List<T>，就可以根据自己定义好的比较原则，进行字段级的过滤了

例如，可以对Person类，进行ＩＤ，与Name的相等来确实整个对象是否与其它实例对象相等：

 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();
        }
    }

如果一个list<person>的实例为

personList，那么，它根据ＩＤ过滤的程序为

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

 

PropertyComparer.cs代码如下

 /// <summary>
    /// 属性比较器
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class PropertyComparer<T> : IEqualityComparer<T>
    {

        private PropertyInfo _PropertyInfo;
        /// <summary>
        /// 通过propertyName 获取PropertyInfo对象        /// </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)
                return 0;
            else
                return propertyValue.GetHashCode();
        }
        #endregion

    }