动态 Linq 查询包含列表 [英] Dynamic Linq query Contains List

问题描述

我使用动态 Linq 进行通用搜索.我有 ID 列表:

I am using dynamic Linq for generic search. I have list of Ids:

List<int> idList = new List<int> { 1, 5, 6};

在普通的 Linq 中，我会这样写:

In plain Linq, I would write:

q = q.Where(a => idList.Contains(a.MyId));

但现在我必须使用System.Linq.Dynamic，因为我事先不知道列的名称.

But now I have to use System.Linq.Dynamic because I don't know in advance name of the column.

string someId = "CustomId";
q = q.Where("@0"+ ".Contains(" + someId + ")", idList.ToArray());

但这会导致错误:

类型 'Int32' 中不存在适用的方法 'Contains'"

"No applicable method 'Contains' exists in type 'Int32'"

我怎样才能做到这一点?

How can I achieve this?

是否有一些扩展库为 dynamic Linq 或其他方式实现了 Contains.

Is there some extension library that implements Contains for dynamic Linq or some other way.

推荐答案

你可以写这样的东西来动态构建你的查询函数:

You could write something like this that builds your query function dynamically:

public static Func<ObjT, bool> PropertyCheck<ObjT, PropT>(string propertyName, Expression<Func<PropT, bool>> predicate)
{
    var paramExpr = Expression.Parameter(typeof(ObjT));
    var propExpr = Expression.Property(paramExpr, propertyName);
    return Expression.Lambda<Func<ObjT, bool>>(Expression.Invoke(predicate, propExpr), paramExpr).Compile();
}

然后，它可以像这样使用:

Then, it could be used like this:

foos.Where(PropertyCheck<Foo, int>("MyId", x => idList.Contains(x)));

当然，您也可以提供自己的 Where 扩展方法来一次性完成所有操作:

Of course, you could also just provide your own Where extension method that does all that at once:

public static IEnumerable<T> Where<T, PropT>(this IEnumerable<T> self, string propertyName, Expression<Func<PropT, bool>> predicate)
{
    var paramExpr = Expression.Parameter(typeof(T));
    var propExpr = Expression.Property(paramExpr, propertyName);
    return self.Where<T>(Expression.Lambda<Func<T, bool>>(Expression.Invoke(predicate, propExpr), paramExpr).Compile());
}

foos.Where<Foo, int>("MyId", x => idList.Contains(x));

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