linq-to-entities

问题 I have this Linq to object query: var result = Users.Where(u => u.Address.Country.Code == 12) I get an exception if the Address or the Country are null. Why this query doesn't check if the address is null and just after that procced? This way I won't need to write this terrible query: var result = Users.Where(u => u.Address != null && u.Address.Country != null && u.Address.Country.Code == 12) In Linq to SQL the first query wiil do the job(from other reasons of course). Is the a way to avoid

问题 I have this Linq to object query: var result = Users.Where(u => u.Address.Country.Code == 12) I get an exception if the Address or the Country are null. Why this query doesn't check if the address is null and just after that procced? This way I won't need to write this terrible query: var result = Users.Where(u => u.Address != null && u.Address.Country != null && u.Address.Country.Code == 12) In Linq to SQL the first query wiil do the job(from other reasons of course). Is the a way to avoid

问题 I'm not sure about Navigational Properties in EF 4 so I would kindly ask you an explanation. Lets imagine this scenarios: A) I have two Entities A and B with a relation N to N (many to many) and tree Table in my Data Base A and B and a Link Table AB with two Foreign Key . In this scenario EF create a Navigational Property lets call it X and also a XReference . B) I have two Entities A and B with a relation 1 to N (one to many) and two Table in my Data Base A and B with one Foreign Key . In

问题 I have the following LINQ query: var result = from person in dbContext.Person select new { FirstName = person.FirstName, LastName = person.LastName, // I want to save this logic JobCount = person.Jobs.Count(x => x.Completed) }; } To avoid repeating myself in other LINQ queries, I would like to make the JobCount lambda logic available for use in other queries. I thought I might be able to use Func<Person, int> , like so: public Func<Person, int> GetCompletedJobsForPerson = person => person

问题 This throws an error 'ArrayIndex' is not supported in LINQ to Entities. so what would be an alternative for this as the split and replace fails? from S in db.Students where S.ID = ID select new { S.EMAIL.Split('@')[0].Replace(".", " ,"), S.NAME }; This is for a list of Students and this is how I currently can add them. mylist.DataValueField = "email"; mylist.DataTextField = "name"; This fails: S.EMAIL.Split('@')[0].Replace(".", " ,") Please help. Thanks 回答1: If you want it to run on the SQL

问题 This throws an error 'ArrayIndex' is not supported in LINQ to Entities. so what would be an alternative for this as the split and replace fails? from S in db.Students where S.ID = ID select new { S.EMAIL.Split('@')[0].Replace(".", " ,"), S.NAME }; This is for a list of Students and this is how I currently can add them. mylist.DataValueField = "email"; mylist.DataTextField = "name"; This fails: S.EMAIL.Split('@')[0].Replace(".", " ,") Please help. Thanks 回答1: If you want it to run on the SQL

问题 I'm using LINQ to Entities My GridView is the following : <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" AllowPaging="True" EmptyDataText="No Data" CellPadding="3" CellSpacing="1" AllowSorting="True" OnPageIndexChanging="GridView1_PageIndexChanging" OnRowCancelingEdit="GridView1_RowCancelingEdit" OnRowEditing="GridView1_RowEditing" OnRowUpdating="GridView1_RowUpdating" CssClass="gridview" OnSorting="GridView1_Sorting" HorizontalAlign="Center"> <AlternatingRowStyle

问题 Here's a bunch of things I tried... hopefully you can extrapolate from it what I'm trying to do and what I'm doing wrong. Okay so I'm having problems with loading related entities when using this DoQuery: public ObjectQuery<E> DoQuery(ISpecification<E> where) { return (ObjectQuery<E>)_ctx.CreateQuery<E>("[" + typeof(E).Name + "]").Where(where.EvalPredicate); } If I just use this, I end up getting an object back that contains all proper parameters except the ones that are related entities...

问题 Imagine you've got some Entity Framework entities that look like this (obviously not these specific classes, but the autogenerated ones with all the Entity Framework plumbing; these are just for illustration): public class Parent { public int ID { get; set; } public List<Child> Children { get; set; } } public class Child { public int ID { get; set; } public Parent Parent { get; set; } public int Number { get; set; } } I have a LINQ query that looks like this: from parent in context.Parents

问题 In my project I use Entity Framework 4.4.0.0 and I have the following dilemma. I have to check if an user is activated. My query looks like: Any() _context.Users.Any(u => u.Id == userId && u.IsActivated); The generated sql is: SELECT CASE WHEN ( EXISTS (SELECT 1 AS [C1] FROM [dbo].[Users] AS [Extent1] WHERE ( [Extent1].[Id] = @p__linq__0 ) AND ( [Extent1].[IsActivated] = 1 )) ) THEN cast(1 AS BIT) WHEN ( NOT EXISTS (SELECT 1 AS [C1] FROM [dbo].[Users] AS [Extent2] WHERE ( [Extent2].[Id] = @p_