linq-to-entities

问题 I have a table with a constraint on one field - it can be 1, 2 or 3. (The correct solution to this is probably to create a lookup table for this, but for now I'm wondering if it's possible to do this without the lookup table.) I've created a class that returns an IEnumerable for the values. I'm using LINQ to Entities, and would like to be able to display the text value in a col. when listing all the entities. The code for create/edit looks like: Controller.cs: ViewData["Message_Types"] =

问题 I have a table with a constraint on one field - it can be 1, 2 or 3. (The correct solution to this is probably to create a lookup table for this, but for now I'm wondering if it's possible to do this without the lookup table.) I've created a class that returns an IEnumerable for the values. I'm using LINQ to Entities, and would like to be able to display the text value in a col. when listing all the entities. The code for create/edit looks like: Controller.cs: ViewData["Message_Types"] =

问题 I just upgraded to VS 2013 and also started a new MVC project, and am being faced with 99% CPU usage for a couple minutes by IIS while debugging on my local PC. (Happens in both Release and Debug mode) I just realized that the problem is proportional to the number of lines returned by by Linq Query. If I use Take(1) or Take(10) it's fine. If I use Take(100) the problem occurs. Here is my actionresult (with private info altered): public ActionResult Summary(string daystoshow, DateTime? day =

问题 I am trying to figure out the best way of getting the record count will incorporating paging. I need this value to figure out the total page count given a page size and a few other variables. This is what i have so far which takes in the starting row and the page size using the skip and take statements. promotionInfo = (from p in matches orderby p.PROMOTION_NM descending select p).Skip(startRow).Take(pageSize).ToList(); I know i could run another query, but figured there may be another way of

问题 I'm looking for confirmation/clarification with these LINQ expressions: var context = new SomeCustomDbContext() // LINQ to Entities? var items = context.CustomItems.OrderBy(i => i.Property).ToList(); // LINQ to Objects? var items2 = context.CustomItems.ToList().OrderBy(i => i.Property); (Q1) Am I correct in thinking the first method is LINQ to Entities where EF builds a more specific SQL statement to pass on, putting the ordering effort on on the database? (Q2) Is the second method LINQ to

问题 I have an entity object 'User' which implements 'IUser': IQueryable<User> users = Db.User; return users; But what I actually want to return is: IQueryable<IUser> So what is the best way to convert IQueryable<User> to IQueryable<IUser> without actually running the query? Right now I am doing this but it seems like a hack: IQueryable<IUser> users = Db.User.Select<User, IUser>(u => u); 回答1: Your "hacky" solution looks fine to me. 来源： https://stackoverflow.com/questions/1240087/what-is-the-best

问题 I have data that looks like so: UserId | SongId -------- -------- 1 1 1 4 1 12 2 95 I also have the following class: class SongsForUser { public int User; public List<int> Songs; } What I would like to do is use LINQ to select from my data to create a collection of SongsForUser objects. Below is what I have come up with so far: var userCombos = songs.UserSongs.Select(x => new SongsForUser() { User = x.UserId, Songs = /*What goes here?*/ }); How would I go about populating my Songs List? So

问题 I have the following code DateTime now = DateTime.UtcNow; var allItemsOver64 = _inventoryContext.Items.Where(i => (SqlFunctions.DateDiff("dd", i.PrimaryInsured.DoB, now) / 365.0) >= 65); IQueryable<Item> items65To69 = allItemsOver64.Where(i => (SqlFunctions.DateDiff("dd", i.PrimaryInsured.DoB, now) / 365.0) >= 65 && (SqlFunctions.DateDiff("dd", i.PrimaryInsured.DoB, now) / 365.0) <= 69); But when I try and use allItemsOver64 thus Items65To69.Count() I get this error The expression ((((Convert

问题 I have a few (fairly redundant) queries in my app that are something like this: var last30Days = DateTime.Today.AddDays(-30); from b in Building let issueSeverity = (from u in Users where u.Building == b from i in u.Issues where i.Date > last30Days select i.Severity).Max() select new { Building = b, IssueSeverity = issueSeverity } And: var last30Days = DateTime.Today.AddDays(-30); from c in Countries let issueSeverity = (from u in Users where u.Building.Country == c from i in u.Issues where i

问题 I have database and in it I have class hotel with gps coordinates. I want to get closest places to coordinates which I choose. I think It should look like this (I found many example codes here and like this one): var coord = new GeoCoordinate(latitude, longitude); var nearest = (from h in db.hotels let geo = new GeoCoordinate(h.gps.lat, h.gps.lng) orderby geo.GetDistanceTo(coord) select h).Take(10); The problem is that I have this error when I tried to search for something: Only parameterless