Articles

Cannot construct entity

Cannot Construct Entity...Exception: The entity cannot be constructed in a LINQ to Entities query...In Entity Framework, mapped entities represent database tables, and Entity Framework doesn't allow to project on a mapped entity in a LINQ to Entities query. If you project on a mapped entity, then it will partially load an entity, which is not a valid state. EF won't have any clue how to handle when the entity is updated....using (var context = new CustomerContext()) { var customer = context...

Concurrency

Concurrency...Exception: Store update, insert, or delete statement affected an unexpected number of rows (0)...A concurrency conflict occurs when one user displays an entity's data in order to edit it, and then another user updates or deletes the same entity's data before the first user's change is written to the database....Another case for this exception is when a new object is created and and it's state is set to modified the EntityState.Modified....using (var context = new EntityContext()) {...

DataReader already open

DataReader already Open...Exception: There is already an open DataReader associated with this Command which must be closed first...When executing the following code....foreach (var blog in blogs) { blog.Name += " updated"; blog.Url += " updated"; context.SaveChanges(); } ...It gives the following exception....InvalidOperationException: There is already an open DataReader associated with this Command which must be closed first....StackOverflow Related Questions...There is already an o...

Entity Type has not key defined

EntityType Has No Key Defined...Exception: One or more validation errors were detected during model generation. EntityType has no key defined. Define the key for this EntityType....StackOverflow Related Questions...EntityType has no key defined error...mvc entity type has no key defined...Entity type has no key defined EF6...Answer...There are several reasons this can happen and you can fix it very easily when this message occurs....Scenario 1:...You've forgotten to include a key....public class...

LINQ does not recognize method

LINQ Does Not Recognize Method...Exception: LINQ to Entities does not recognize the method...It is the most common exception occurs when working with entity framework and converting data inside IQueryable result for filtering....using (var context = new CustomerContext()) { var item = context.InvoiceItems .Where(i => i.Code == code.ToString()) .FirstOrDefault(); } ...StackOverflow Related Questions...Why LINQ to Entities does not recognize the method 'System.String ToString()...

Not found in ObjectStateManager

Not Found in ObjectStateManager...Exception: The object cannot be deleted because it was not found in the ObjectStateManager...When an entity is fetched and deleted using different DbContext object, then it throws an exception ...The object cannot be deleted because it was not found in the ObjectStateManager....Customer deletedCustomer = null; using (var context = new EntityContext()) { deletedCustomer = context.Customers.Where(c => c.CustomerID == 3).FirstOrDefault(); } using (var context ...

Only primitive types supported

Only Primitive Types Supported...Exception: Unable to create a constant value of type [Object]. Only primitive types or enumeration types are supported in this context....Using lambda expression, there are certain things that you can express in C#, but Entity Framework doesn't know how to convert it to SQL. For example, retrieve all the invoices of any particular customer....using (var context = new CustomerContext()) { var invoices = context.Invoices .Where(i => i.Customer == custom...

Specified property not supported

Specified Property Not Supported...Exception: The specified type member '[ColumnName]' is not supported in LINQ to Entities Exception...Entity Framework can't filter data based on a property on the server side which is not a part of the table schema. It means that Entity Framework can't convert not mapped a property to SQL....The following example is trying to filter the customers on TotalInvoices, but the TotalInvoices property is not mapped to database....using (var context = new EntityContext...

Specified type not supported

Specified Type Not Supported...Exception: The specified type member '[MemberName]' is not supported in LINQ to Entities...Entity Framework cannot convert some data types to SQL such as DateTime.Date....using (var context = new EntityContext()) { var fromDate = DateTime.Now.AddDays(-7).Date; var customer = context.Customers.Where(c => c.CustomerID == 1) .Include(c => c.Invoices) .Where(c => c.Invoices.Any(i => i.InvoiceDate.Date >= fromDate)) .FirstOrDefault(); } ...