ASP.NET EF LINQ - 按标签搜索

Question

I need to search database users by tags. One user has many tags and one tag is shared by many users. But when I search by specific set of tags I want want users that have all these tags but can have tags that I do not search for ofc. Here were my tries:

return context.Contacts.Include("Tags").Where(c => c.Tags.**Any**(t => tagIds.Contains(t.Id.ToString()))).ToList();
//Above approach would search kind of union between tags. It would not converge. Meaning if I have user1 with tags A and B and user2 with B and C  And I search by A and B i would get both users, even though i want only user1

//Bellow apporach would search too strict, meaning if user contains tags A and B and i search by tag A this user would not be showed

 return context.Contacts.Include("Tags").Where(c => c.Tags.**All**(t => tagIds.Contains(t.Id.ToString()))).ToList();

Answer 1

You could use the PredicateBuilder class provided in the LinqKit package

In your package manager console:

Install-Package LinqKit

And then use the PredicateBuilder as follows:

var predicate = PredicateBuilder.True<Contact>();
foreach (var tagId in tagIds)
{
    predicate = predicate.Or(c => c.Tags.Any(tag => tag.Id.ToString() == tagId));
}

var contactsByTags = context.Contacts.Include("Tags").Where(predicate).ToList();