Lambda 表达式中使用 Contains （where in）

public static class QueryableExtension

    {

        private static Expression<Func<TElement, bool>> GetWhereInExpression<TElement, TValue>(Expression<Func<TElement, TValue>> propertySelector, IEnumerable<TValue> values)

        {

            ParameterExpression p = propertySelector.Parameters.Single();

            if (!values.Any())

                return e => false;

            var equals = values.Select(value => (Expression)Expression.Equal(propertySelector.Body, Expression.Constant(value, typeof(TValue))));

            var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));

            return Expression.Lambda<Func<TElement, bool>>(body, p);

        }

        /// <summary>  

        /// Return the element that the specified property's value is contained in the specifiec values  

        /// </summary>  

        /// <typeparam name="TElement">The type of the element.</typeparam>  

        /// <typeparam name="TValue">The type of the values.</typeparam>  

        /// <param name="source">The source.</param>  

        /// <param name="propertySelector">The property to be tested.</param>  

        /// <param name="values">The accepted values of the property.</param>  

        /// <returns>The accepted elements.</returns>  

        public static IQueryable<TElement> WhereIn<TElement, TValue>(this IQueryable<TElement> source, Expression<Func<TElement, TValue>> propertySelector, params TValue[] values)

        {

            return source.Where(GetWhereInExpression(propertySelector, values));

        }

        /// <summary>  

        /// Return the element that the specified property's value is contained in the specifiec values  

        /// </summary>  

        /// <typeparam name="TElement">The type of the element.</typeparam>  

        /// <typeparam name="TValue">The type of the values.</typeparam>  

        /// <param name="source">The source.</param>  

        /// <param name="propertySelector">The property to be tested.</param>  

        /// <param name="values">The accepted values of the property.</param>  

        /// <returns>The accepted elements.</returns>  

        public static IQueryable<TElement> WhereIn<TElement, TValue>(this IQueryable<TElement> source, Expression<Func<TElement, TValue>> propertySelector, IEnumerable<TValue> values)

        {

            return source.Where(GetWhereInExpression(propertySelector, values));

        }  

    }

 

使用方法

 

public List<Activity> Select(List<int> projectList, List<int> activityTypeList)

{  

    var result = ObjectContext.Activity.

                WhereIn(it => it.Project.ProjectID, projectList).WhereIn(it => it.ActivityType.ActivityTypeID, activityTypeList);

    return result.ToList();

}