使用 Linq 查询选择属性的任何值与列表中的值匹配的对象

Question

So I am trying to filter the modules object list by userID of the currently logged in user. After that I am trying to take the moduleID of those selected object.

Using that I want to filter the reports list to only those that contain a moduleID that matches any of the the previously obtained list of moduleID .

I'm not that particularly knowledgeable on Linq and this is what I came up with:

    var name = User.Identity.GetUserName();
        //gets the currently logged in user:
        ApplicationUser currentUser = 
            (ApplicationUser)db.Users.Single(x => x.UserName == name); 
        //gets moduleID's for modules owned by current user:
        var modules = (from i in db.Modules
                       where i.User == currentUser
                       select i.ModuleID); 
        var Reports = from u in db.Reports
                      where u.moduleID == modules
                      select u;

I'm having problems with the last portion trying to incorporate the contains method into the statement.

Any help would be appreciated.

Answer 1

You could simplify the multiple queries to one if I'm inferring your table structure correctly:

var name = User.Identity.GetUserName();
var reports = from r in db.Reports
              join m in db.Modules on r.moduleID equals m.ModuleID
              where m.User.UserName == name
              select r;

Answer 2

You can't compare a int to a IEnumerable<int> . However you can check if the moduleID is found within the modules like this :

where modules.Contains(u.moduleID)

Answer 3

You're on the right track.

var Reports = from u in db.Reports
              where modules.Contains(u.moduleID)
              select u;

Or using lambda:

var reports = db.Reports.Where(u => modules.Contains(u));

Answer 4

You're close. In Linq its a little backwards from standard SQL. In its case you want to see if the report's module id is contained in the list of modules, so it would look like this:

  var Reports = from u in db.Reports
                where modules.Contains(u.moduleID)
                select u;

Answer 5

Use the navigation properties if you have a one to many relation you could do directly in your Where clause:

var name = User.Identity.GetUserName();
var Reports = db.Reports.Where(x => x.Module.User.Name == name);