linq-to-entities

问题 I have an issue trying to maximize the performance of our listview that has pages. I want the entity framework to do a select statement, but only return a range of the result (range = the items of one page of the listview). I have searched google but didn't find any results on this. I only found that I can do a .ToList().GetRange(start index, end index), but then all items would be loaded in memory, and that is what I would like to avoid... Can someone tell me if this can be done? (I don't

问题 I have just started using EF and found it cool, but I ran into a problem, Problem: I changed my DB schema of a column inside the table User, It was Varbinary(50) previously I then changed it into VarChar(50), and then inside the MyModel.edmx designer I chose "Update model from database", after clicking finish I received this error. Error: Error 2019: Member Mapping specified is not valid. The type 'Edm.Binary [Nullable=False,DefaultValue=,MaxLength=100,FixedLength=False]' of member 'Email' in

问题 How would i write something like this in linq to entities sb.Append(" WHERE question.question_isdeleted = 0"); if (catid != 0) sb.AppendFormat(" AND (CatID IN ({0}))", catsSTR); if(!string.IsNullOrEmpty(AuthorID)) sb.Append(" AND (question_ownerid = @id)"); i think I just need the syntax to write an if conditional in linq to entities 回答1: I would use dot notation here: var query = questions.Where(q => !q.IsDeleted); if (catId != 0) { query = query.Where(q => cats.Contains(q.CatID)); } if

问题 I am using a view to return a complex search query. When I usin linq to query against EF it is returning the same row 3 times(the actual rowcount is correct). using LinqPad I have run the same linq against my ef entity and the actual database view. ReadmitPatientList .AsQueryable() .Where("PatientLastName.StartsWith(\"cooper\")") .OrderBy (rpl => rpl.PatientLastName) .Dump(); That is the linq I am using for both. linqpad shows the lambda as this: EF: ReadmitPatientList.MergeAs (AppendOnly)

问题 Problem Need to convert int to string using EF4 + SQL CE4. The recommended option of using SqlFunctions.StringConvert(double) still gives me errors. Option 1 (original). This gives me error: public static IEnumerable<SelectListItem> xxGetCustomerList() { using (DatabaseEntities db = new DatabaseEntities()) { var list = from l in db.Customers orderby l.CompanyName select new SelectListItem { Value = l.CustomerID.ToString(), Text = l.CompanyName }; return list.ToList(); } } Option 2 (most

问题 I've got the following query: model.Page = db.Pages .Where(p => p.PageId == Id) .Include(p => p.Series .Select(c => c.Comics .Select(col => col.Collection))) .SingleOrDefault(); This works great, although I now need to order the Comics by a property called 'ReadingOrder'. I've tried: model.Page = db.Pages .Where(p => p.PageId == Id) .Include(p => p.Series.Select(c => c.Comics.OrderBy(o => o.ReadingOrder) .Select(col => col.Collection))) .SingleOrDefault(); But this results in the following

问题 I am working with a third party database and need to select a distinct set of data for the specific market that I am looking into. The data is the same for each market, so it is redundant to pull it all in, and I don't want to hardcode any logic around it as we are working with the vendor to fix the issue, but we need a fix that will work with the vendors fix as well as the way the database is currently as it could be some time before thier fix goes live. I do not want to group by anything as

问题 Why does one method work but not the other, when it seems they are both doing the same thing, i.e. constructing an entity. My question then, is there a way to construct the entity in a L2E query instead of having to use just Linq or indeed both? This works fine... var queryToList = (from ac in ctx.AuthorisationChecks where wedNumbers.Contains(ac.WedNo) orderby ac.WedNo, ac.ExpAuthDate, ac.ActAuthDate select new AuthorisationCheck { Blah = ac.Blah }).ToList(); model.AuthorisationChecks =

问题 When using LINQ to entity doing string comparisons will ignore white spaces. In my table, I have an nchar(10) column so any data saved if it is not 10 characters will fill the rest with empty spaces. Below i am comparing the "ncharTextColumn" with the "Four" string. And even though the ncharText will equal "Four " It results in a match and the "result" variable will contain 1 record TestEntities1 entity = new TestEntities1(); var result = entity.Table_1.Where(e => e.ncharText == "Four"); Is

问题 I have a Document class that stores the data of that document as a byte array. I need to check the size of the array, using LINQ to Entities. I have tried the following: [long Linq query here...] o.Data.Length < 800000) The problem is I get the following exception: The LINQ expression node type 'ArrayLength' is not supported in LINQ to Entities." Is there any other way to check the size of the byte array? 回答1: Use SqlFunctions.DataLength Method (Byte[]) to compare length. yourquery.....