entity-framework

问题 I am trying to replace my big, ugly query; although ugly it works as desired:- using (var ctx = new Data.Model.xxxTrackingEntities()) { var result = ctx.Offenders .Join(ctx.Fees, o => o.OffenderId, f => f.OffenderId, (o, f) => new { Offenders = o, Fees = f }) .Join(ctx.ViolationOffenders, o => o.Fees.ViolationId, vo => vo.ViolationId, (o, vo) => new { Offenders = o, ViolationOffenders = vo }) .Join(ctx.Violations, v => v.ViolationOffenders.ViolationId, vo => vo.ViolationId, (v, vo) => new {

问题 I have an issue when adding entities with multiple one-to-one relationship with the same table in Entity Framework Core. Based on this question I have the following things: public class Article { public int Id { get; set; } public int? PreviousId { get; set; } public Article Previous { get; set; } public int? NextId { get; set; } public Article Next { get; set; } } In the OnModelCreating of the DbContext as I have: protected override void OnModelCreating(ModelBuilder modelBuilder) { base

问题 I created some new tables and I noticed I didn't use the good naming convention for the ids. So I did a new add-migration with the new ids but when I try to update-database I have the following error : The constraint 'PK_dbo.DB_User_Type' is being referenced by table 'AspNetUsers', foreign key constraint 'FK_dbo.AspNetUsers_dbo.DB_User_Type_DB_User_Type_Id'. Could not drop constraint. See previous errors. I don't understand because the script starts by dropping all constraints. Could someone

问题 I am using Unit of work and Repository pattern along with EF6 in my asp.net web application. DbContext object is getting created and destroyed on every request. I am thinking that it is costly creating the new dbcontext on every request(I have not done any performance bench marking). Is this cost of creating DbContext on every request can be ignored ? Does anybody done some bench marking? 回答1: Creating a new context is ridiculously cheap, on the order of about 137 ticks on average (0.0000137

问题 I am using Unit of work and Repository pattern along with EF6 in my asp.net web application. DbContext object is getting created and destroyed on every request. I am thinking that it is costly creating the new dbcontext on every request(I have not done any performance bench marking). Is this cost of creating DbContext on every request can be ignored ? Does anybody done some bench marking? 回答1: Creating a new context is ridiculously cheap, on the order of about 137 ticks on average (0.0000137

问题 I'm trying to rewrite old library to use EntityFramework Core and I can't figure out how to begin transaction with specific isolation level. Previously I was able to do something like this: DbContext.Database.BeginTransaction(IsolationLevel.Snapshot); What is alternative implementation in the EntityFramework Core? 回答1: The EF Core code is exactly the same. DbContext.Database.BeginTransaction(IsolationLevel.Snapshot); The only difference is that in EF Core the method with isolation level (as

问题 I'm trying to rewrite old library to use EntityFramework Core and I can't figure out how to begin transaction with specific isolation level. Previously I was able to do something like this: DbContext.Database.BeginTransaction(IsolationLevel.Snapshot); What is alternative implementation in the EntityFramework Core? 回答1: The EF Core code is exactly the same. DbContext.Database.BeginTransaction(IsolationLevel.Snapshot); The only difference is that in EF Core the method with isolation level (as

问题 I am developing a web site, it uses SQL Server 2008 R2 Express for its database. And in testing, there is a lot of data and images stored into this database. According to wiki, the SQL Server Express edition has a 10 GB size limit. When I insert data and reach the limit, what exception will be thrown? Or, how do I detect the approaching limit problem by codes ? I use EF 5 with code-first approach to insert large data set. 回答1: In tests I have seen that: sp_spaceused won't work as expected, it

问题 Please consider the following entities public class What { public int Id { get; set; } public string Name { get; set; } public ICollection<Track> Tracks { get; set; } public int? LastTrackId { get; set; }] public Track LastTrack { get; set; } } public class Track { public Track(string what, DateTime dt, TrackThatGeoposition pos) { What = new What { Name = what, LastTrack = this }; } public int Id { get; set; } public int WhatId { get; set; } public What What { get; set; } } I use the

问题 I'm using Entity Framework Code First with Code First migrations. During a migration, I need to create a new table, and then insert some data into it. So I create the table with : CreateTable("MySchema.MyNewTable", c => new { MYCOLUMNID = c.Int(nullable: false, identity: true), MYCOLUMNNAME = c.String(), }) .PrimaryKey(t => t.MYCOLUMNID); Then I try to insert data with : using (var context = new MyContext()) { context.MyNewTableDbSet.AddOrUpdate(new[] { new MyNewTable { MYCOLUMNNAME = "Test"