entity-framework

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 want a solution to this problem that does not involve ToUpper or ToLower, as I use in the code below; var upper = term.ToUpper(); using (var db = this.DataContext) { return db.Counties.Where(x => x.CountyName.ToUpper().Contains(upper)).ToList(); } I am using entitly framework so the C# solution of using StringComparison.CurrentCultureIgnoreCase does not work. It does work for Equals , EndsWith and StartsWith , but not Contains . 回答1: I use EF6 and Sql Server and Contains is mapped to LIKE '

问题 I want a solution to this problem that does not involve ToUpper or ToLower, as I use in the code below; var upper = term.ToUpper(); using (var db = this.DataContext) { return db.Counties.Where(x => x.CountyName.ToUpper().Contains(upper)).ToList(); } I am using entitly framework so the C# solution of using StringComparison.CurrentCultureIgnoreCase does not work. It does work for Equals , EndsWith and StartsWith , but not Contains . 回答1: I use EF6 and Sql Server and Contains is mapped to LIKE '

问题 I have enabled automatic migrations. Then, I deleted my whole db. Next, i executed Update-database from command console, and it recreated my db. Then, I started my application only to see this error: Model compatibility cannot be checked because the database does not contain model metadata. Model compatibility can only be checked for databases created using Code First or Code First Migrations. So what exactly is that metadata, and how can I point entity framework to it? PS. My database

问题 I have an extension method to dynamically filter Linq to Entities results using string values. It works fine until I use it to filter nullable columns. Here's my code: public static IOrderedQueryable<T> OrderingHelperWhere<T>(this IQueryable<T> source, string columnName, object value) { ParameterExpression table = Expression.Parameter(typeof(T), ""); Expression column = Expression.PropertyOrField(table, columnName); Expression where = Expression.GreaterThanOrEqual(column, Expression.Constant

问题 We're having a discussion about using Equals or == on an int comparison in a LINQ query. We're using EF4.1 Code First. What is better? var query = context.Boodschappen .Where(b => b.BoodschapID == id).FirstOrDefault(); or: var query = context.Boodschappen .Where(b => b.BoodschapID.Equals(id)).FirstOrDefault(); And why ? 回答1: For Linq To Sql, you want neither. Instead, use Object.Equals: .Where(b => Object.Equals(b.BoodschapID, id) Why? Because of a Bug in the SQL Generator if id happens to be

问题 I'm trying to load related entities of a SingleOrDefault entity, but I am getting the following exception: The navigation property of type IEnumerable is not a single implementation of type ICollection I've tried doing this several ways and ultimately get the same error above for each query against the context (I've included the other ways in comments). using(var context = CustomObjectContextCreator.Create()) { return context.Job.Include("Surveys").Include("SiteInfoes") .Where(r => r.Jobid ==

问题 I have a standard DbContext with code like the following: public DbSet<Interest> Interests { get; set; } public DbSet<User> Users { get; set; } I've recently implemented multi-tenancy by creating a TenantContext that contains the following: private readonly DbContext _dbContext; private readonly Tenant _tenant; public TenantContext(Tenant tenant) : base("name=DefaultConnection") { this._tenant = tenant; this._dbContext = new DbContext(); } public IQueryable<User> Users { get { return

问题 I am using MVC3, C# 4.0 and Entity Framework in Visual Studio 2010. I am generating my edmx and Designed.cs files from a database. I am then generating interfaces from the entities in the Designer.cs file as part of my nLayer structure. The original code is public partial class DataEntrySummary : EntityObject which then becomes public partial class DataEntrySummary : EntityObject, Mb.Interface.IDataEntrySummary My concern is that when the database changes (and it will) and I regenerate the

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 4 years ago . Anyone know a good book or post about how to start in EF? I have seen the DnrTV any other place? 回答1: Mike Taulty's Blog: http://mtaulty.com/CommunityServer/blogs/mike_taultys_blog/archive/category/1024.aspx A great EF intro deck: http://mtaulty.com/CommunityServer/blogs/mike_taultys_blog/archive/2008/03/13