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| using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Data.Objects;
namespace Sample {
public static class Extensions {
public static IQueryable< T > ExtWhereIn<T, TValue>(this ObjectQuery< T > query,
Expression<Func<T, TValue>> valueSelector,
IEnumerable<TValue> values) {
return query.Where(BuildContainsExpression<T, TValue>(valueSelector, values));
}
public static IQueryable< T > ExtWhereIn<T, TValue>(this IQueryable< T > query,
Expression<Func<T, TValue>> valueSelector,
IEnumerable<TValue> values) {
return query.Where(BuildContainsExpression<T, TValue>(valueSelector, values));
}
private static Expression<Func<TElement, bool>> BuildContainsExpression<TElement, TValue>(
Expression<Func<TElement, TValue>> valueSelector, IEnumerable<TValue> values) {
if (null == valueSelector) { throw new ArgumentNullException("valueSelector"); }
if (null == values) { throw new ArgumentNullException("values"); }
ParameterExpression p = valueSelector.Parameters.Single();
// p => valueSelector(p) == values[0] || valueSelector(p) == ...
if (!values.Any()) {
return e => false;
}
var equals = values.Select(value => (Expression)Expression.Equal(valueSelector.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);
}
}
class Program {
static void Main(string[] args) {
List<int> fullList = new List<int>();
for (int i = 0; i < 20; i++) {
fullList.Add(i);
}
List<int> filter = new List<int>();
filter.Add(2);
filter.Add(5);
filter.Add(10);
List<int> results = fullList.AsQueryable().ExtWhereIn<int, int>(item => item, filter).ToList();
foreach (int result in results) {
Console.WriteLine(result);
}
}
}
} |