如何在Linq中使用字符串数组All运算符

Question

My query is as follows:

string[] keys = txtSearch.Text.Split(' ');

var query = (from m in db.Messages
             join r in db.Recievers on m.Id equals r.Message_Id
             where (keys.All(k => (m.MessageText + m.Comments.Select(cmt => cmt.CommentText).ToString()).Contains(k)))
             select m.Id).Distinct();

I get the following error:

Local sequence cannot be used in LINQ to SQL implementation of query operators except the Contains() operator.

Answer 1

The problem is that your query can't be translated to SQL (or at least the provider is not programmed to do so). If fact I don't know how that would query would look in SQL: "Give me all messages where all of these key words are contained in the text or comments"

My first thought is to to multiple requests, one for each key value:

List<int> allIDs = new List<int>();
foreach(string key in keys)
{
    var query = (from m in db.Messages
                 join r in db.Recievers on m.Id equals r.Message_Id
                 where m.MessageText.Contains(key) || m.Comments.Any(cmt => cmt.CommentText.Contains(key)
                 select m.Id).Distinct();
    allIds.AddRange(query);
}

but you may even need to search for messages and comments in separate queries.

obviously you'd prefer to do it in one query, but I don't see how that can be done in SQL without using cursors anyways. If you can come up with a SQL statement that gives you the right results, then it may be easier to just call that SQL statement directly rather than trying to come up with a Linq statement that is compiled to equivalent SQL.

Answer 2

You can only use Array.Contains() in linq to SQL queries when using local collections.

You need to change your query based on this rule.

Answer 3

The All operator returns a boolean, it also determines if all elements satisfy a condition. As you're enumerating, as soon as a condition isn't met, the enumeration stops and returns a true or false.

I believe you're expecting a Where functionality, return all the specified elements that satisfy a match on your search.

I don't believe you're utilizing the query correctly.