I am getting this error when I GetById() on an entity and then set the collection of child entities to my new list which comes from the MVC view. The operation failed: The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a … Read more
I have this query: int maxShoeSize = Workers .Where(x => x.CompanyId == 8) .Max(x => x.ShoeSize); What will be in maxShoeSize if company 8 has no workers at all? UPDATE: How can I change the query in order to get 0 and not an exception? 11 Answers 11
I’m using EF 6.0 for my project in C# with manual migrations and updates. I have about 5 migrations on the database, but I realised that the last migration was bad and I don’t want it. I know that I can rollback to a previous migration, but when I add a new (fixed) migration and … Read more
I have a SQL Server table in Entity Framework named employ with a single key column named ID. How do I delete a single record from the table using Entity Framework? 15 Answers 15
I have a project that uses Entity Framework. While calling SaveChanges on my DbContext, I get the following exception: System.Data.Entity.Validation.DbEntityValidationException: Validation failed for one or more entities. See ‘EntityValidationErrors’ property for more details. This is all fine and dandy, but I don’t want to attach a debugger every time this exception occurs. More over, in … Read more
In using the EntityFramework, I get the error “A lambda expression with a statement body cannot be converted to an expression tree” when trying to compile the following code: Obj[] myArray = objects.Select(o => { var someLocalVar = o.someVar; return new Obj() { Var1 = someLocalVar, Var2 = o.var2 }; }).ToArray(); I don’t know what … Read more
I was using an .mdf for connecting to a database and entityClient. Now I want to change the connection string so that there will be no .mdf file. Is the following connectionString correct? <connectionStrings> <!–<add name=”conString” connectionString=”metadata=res://*/conString.csdl|res://*/conString.ssdl|res://*/conString.msl;provider=System.Data.SqlClient;provider connection string="Data Source=.\SQL2008;AttachDbFilename=|DataDirectory|\NData.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True;MultipleActiveResultSets=True"” providerName=”System.Data.EntityClient” />–> <add name=”conString” connectionString=”metadata=res://*/conString.csdl|res://*/conString.ssdl|res://*/conString.msl;provider=System.Data.SqlClient;provider connection string="Data Source=.\SQL2008;Initial Catalog=NData;Integrated Security=True;Connect Timeout=30;User Instance=True;MultipleActiveResultSets=True"” … Read more
Let’s just suppose I have a valid need for directly executing a sql command in Entity Framework. I am having trouble figuring out how to use parameters in my sql statement. The following example (not my real example) doesn’t work. var firstName = “John”; var id = 12; var sql = @”Update [User] SET FirstName … Read more
is there “elegant” way to give specific property a default value ? Maybe by DataAnnotations, something like : [DefaultValue(“true”)] public bool Active { get; set; } Thank you. 17 Answers 17
I’m (re)designing large-scale application, we use multi-layer architecture based on DDD. We have MVC with data layer (implementation of repositories), domain layer (definition of domain model and interfaces – repositories, services, unit of work), service layer (implementation of services). So far, we use domain models (mostly entities) across all layers, and we use DTOs only … Read more
