linq-to-entities

问题 I have a Linq query that queries the following tables: Tasks with a one-to-many link to: TaskLinks and TaskLinks has a one-to-one link to a Table called Entities. I am trying to select the task, eager load (via .Include) the TaskLinks and select the Entity linked to the TaskLink. But I need to filter the Task (by Access Level int) and the TaskLinks so that I don't include any Inactive (bool) records. Here is my Linq query: Tasks.Where(t => t.AccessLevel <= 5) .Include(tl => tl.TaskLinks.Where

问题 I am trying to understand some performance implication of Linq from this free ebook by RedGate ftp://support.red-gate.com/ebooks/under-the-hood-of-net-memory-management-part1.pdf On page 157-158 in this book, they created following example. Order[] pastDueAccounts = null; DateTimedueDate = DateTime.Today.AddDays(-7); using(varcontext = new Context()) { pastDueAccounts = context.Accounts.Where(account => account.DueDate < dueDate).ToArray(); } They then re-factored part of lamda expression

问题 i heard people saying date time comparison do not work just due to time part because datetime has time part. in sql i always compare datetime like this way and it works fine select * from employee where convert(varchar,dob,112) > '20111201' // this yyyymmdd format. how could i simulate this in a LINQ query? 回答1: The one thing to keep in mind is that operations on DateTime structs that represent database columns don't translate to SQL. So, you cannot write a query like: from e in

问题 maybe foolish question, first times with linq to entities (well, linq in general). table with id(int), value(decimal), name(string) for each record i need id list<string> id value name THE FOLLOWING WORKS FINE int pageSize=10 int pageIndex=2 var data = (from c in db.Customers orderby c.ID select new { c.ID, c.Value, c.Name } ).Skip(pageSize * pageIndex).Take(pageSize).ToArray(); but doesn'organize the data in the way i need them. However the results are like: 1 100 name A 2 300 name B 3 200

问题 i'm using EF 4.4.20627.0 with MySQL 5.6 , MySQL .net connector version 6.6.4 i have a method like this, which generated sql is very very slow (needs more than 1 min) private List<TNews> GetPagedNews(int pagenum, int pagesize, AdvSearcherArgs advcArgs, string keyword) { var dataSrc = _dbRawDataContext.TNews.Where(x => x.Id>0); if (!string.IsNullOrWhiteSpace(advcArgs.PMAC)) { dataSrc = dataSrc.Where(m => m.Pmac == advcArgs.PMAC); } if (!string.IsNullOrWhiteSpace(advcArgs.BegineDate)) { var

问题 i'm using EF 4.4.20627.0 with MySQL 5.6 , MySQL .net connector version 6.6.4 i have a method like this, which generated sql is very very slow (needs more than 1 min) private List<TNews> GetPagedNews(int pagenum, int pagesize, AdvSearcherArgs advcArgs, string keyword) { var dataSrc = _dbRawDataContext.TNews.Where(x => x.Id>0); if (!string.IsNullOrWhiteSpace(advcArgs.PMAC)) { dataSrc = dataSrc.Where(m => m.Pmac == advcArgs.PMAC); } if (!string.IsNullOrWhiteSpace(advcArgs.BegineDate)) { var

问题 We have a table called Student . That table has a field called Homeroom , where the value is a room number of the student's homeroom. The value can be null. We have a second table called Staff . That table also has a field called Homeroom to indicate which homeroom the teacher is assigned to. The value can be null. But when the student's Homeroom is null, a Staff record should not be returned. We used to take advantage of the fact that checking two null fields for equality always returns

问题 We have a table called Student . That table has a field called Homeroom , where the value is a room number of the student's homeroom. The value can be null. We have a second table called Staff . That table also has a field called Homeroom to indicate which homeroom the teacher is assigned to. The value can be null. But when the student's Homeroom is null, a Staff record should not be returned. We used to take advantage of the fact that checking two null fields for equality always returns

问题 I recently asked a question about tracing Linq-to-Entities I think that one of the answers was not right, as they refer to using the DataContext. Is there a DataContext for LINQ-to-Entities? If so, how do I get it? 回答1: LINQ to Entities uses ObjectContext, not DataContext. Here is a short description of EF: LINQ to Entities, the ObjectContext Class, and the Entity Data Model LINQ to Entities queries use the Object Services infrastructure . The ObjectContext class is the primary class for

问题 With the following table structure (extraneous columns removed) create table [Events] ( ID int not null identity, Name nvarchar(128) not null, constraint PK_Events primary key(ID) ) create table [Donations] ( ID int not null identity, EventID int not null, Amount decimal(10, 2) not null, constraint PK_Donations primary key(ID), constraint FK_Donations_Events foreign key(EventID) references [Events](ID) on update no action on delete no action ) I use the following Linq-to-Entities queries: //