entity-framework

问题 Say I have an entity that I want to query with ranking applied: public class Person: Entity { public int Id { get; protected set; } public string Name { get; set; } public DateTime Birthday { get; set; } } In my query I have the following: Expression<Func<Person, object>> orderBy = x => x.Name; var dbContext = new MyDbContext(); var keyword = "term"; var startsWithResults = dbContext.People .Where(x => x.Name.StartsWith(keyword)) .Select(x => new { Rank = 1, Entity = x, }); var

问题 I am trying to left join on entity frame work 3.5 but i am unable to do so... from i in (from ta in context.test_attempt join uf in context.user_flag on ta.users.USERID equals uf.UserID) select i; I want to use left join instead to join? 回答1: You need to use DefaultIfEmpty() for an outer join: from ta in context.test_attempt join uf in context.user_flag on ta.users.USERID equals uf.UserID into g from uf in g.DefaultIfEmpty() select new { ta, uf } Your outer from/select above is unnecessary,

问题 I am having a really hard time updating and deleting many to many relationships with EF Code-first. I have a fairly simple Model: public class Issue { [Key] public int IssueId { get; set; } public int Number { get; set; } public string Title { get; set; } public DateTime Date { get; set; } public virtual ICollection<Creator> Creators { get; set; } } public class Creator { [Key] public int CreatorId { get; set; } public string FirstName { get; set; } public string MiddleName { get; set; }

问题 I have been following this post on using PostgreSQL with EF6 http://www.jasoncavett.com/blog/postgresql-and-entity-framework-6-code-first/. I have started a brand new MVC5 project hoping to use Postgres in my application for backend. The application starts up fine however when you go to register a user (I selected individual authentication) I get the following error messsage ERROR: 42P01: relation "public.AspNetUsers" does not exist I am unsure as to how to resolve this problem. The error

问题 I have been following this post on using PostgreSQL with EF6 http://www.jasoncavett.com/blog/postgresql-and-entity-framework-6-code-first/. I have started a brand new MVC5 project hoping to use Postgres in my application for backend. The application starts up fine however when you go to register a user (I selected individual authentication) I get the following error messsage ERROR: 42P01: relation "public.AspNetUsers" does not exist I am unsure as to how to resolve this problem. The error

问题 I have a Model that looks like public class Patient { private ICollection<Refill> _refills = new List<Refill>(); public int Id { get; set; } public string FirstName { get; set; } public virtual ICollection<Refill> Refills { get { return _refills; } set { _refills = value; } } public class Refill { public int Id { get; set; } public RefillActivityStatus RefillActivityStatus { get; set; } public DateTime? RefillDate { get; set; } public RefillType RefillType { get; set; } public string RXNumber

问题 So it turns out that I am the last person to discover the fundamental floor that exists in Microsoft's Entity Framework when implementing TPT (Table Per Type) inheritance. Having built a prototype with 3 sub classes, the base table/class consisting of 20+ columns and the child tables consisting of ~10 columns, everything worked beautifully and I continued to work on the rest of the application having proved the concept. Now the time has come to add the other 20 sub types and OMG, I've just

问题 So it turns out that I am the last person to discover the fundamental floor that exists in Microsoft's Entity Framework when implementing TPT (Table Per Type) inheritance. Having built a prototype with 3 sub classes, the base table/class consisting of 20+ columns and the child tables consisting of ~10 columns, everything worked beautifully and I continued to work on the rest of the application having proved the concept. Now the time has come to add the other 20 sub types and OMG, I've just

问题 I have a simple object model as follows... public class Product { public long ProductId { get; set; } public int CategoryId { get; set; } public Category Category { get; set; } } and public class Category { public long CategoryId { get; set; } public List<Product> Products { get; set; } } Generating the underlying database with EntityFramework results in the following schema... Products ProductId CategoryId Category_CategoryId Categories CategoryId In the Products table, the CategoryId column

问题 I have a simple object model as follows... public class Product { public long ProductId { get; set; } public int CategoryId { get; set; } public Category Category { get; set; } } and public class Category { public long CategoryId { get; set; } public List<Product> Products { get; set; } } Generating the underlying database with EntityFramework results in the following schema... Products ProductId CategoryId Category_CategoryId Categories CategoryId In the Products table, the CategoryId column