包含在linq查询中 [英] contains in linq query

问题描述

我正在使用实体框架和LinQ.我有一个名为users的表对象.我有一个名为userids的列表.我必须找到字符串中包含id的所有用户.我必须执行以下操作...

Hi i am using entity framework and LinQ. I have a table objects called users . i have a list called userids. i have to find all users where ids contains in the string. I have to do following operations ...

select * from users where userid in (userids);

我试图这样解决

var u = context.users.Where(o=> usersid.Contains(o=> o.userid)).Select(o=> o);

但是它给出了编译错误.该如何解决?

but it gives compilation error. how to solve this ?

推荐答案

尝试使用此方法:

protected 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();

            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);
}

调用这样的方法:

var u = context.users.Where(BuildContainsExpression<user, Int32>(e => e.Userid, userids)).ToList();

这将解决您的问题.

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