The provider did not return a ProviderManifestToken string Entity Framework
In my case, it was my SQL Server instance that was not running. I simply started the service and everything worked fine. Hope this helps someone down the road.
entity-framework
Entity Framework vs LINQ to SQL
LINQ to SQL only supports 1 to 1 mapping of database tables, views, sprocs and functions available in Microsoft SQL Server. It’s a great API to use for quick data access construction to relatively well designed SQL Server databases. LINQ2SQL was first released with C# 3.0 and .Net Framework 3.5. LINQ to Entities (ADO.Net Entity … Read more
Unable to determine the principal end of an association between the types
That exception is launched because you are trying to configure an one-to-one relationship but you are not specifying which end is the principal in the relationship. Principal end is the one which will be inserted first and which can exist without the dependent one. Dependent end is the one which must be inserted after the principal because it has foreign key to the … Read more
Cannot attach the file *.mdf as database
Take a look at this: Entity Framework don’t create database I would try giving the database a different name. Sometimes you can run into problems with SQL Express when trying to create a database with the same name a second time. There is a way to fix this using SQL Server Management Studio but it’s … Read more
entity object cannot be referenced by multiple instances of IEntityChangeTracker. while adding related objects to entity in Entity Framework 4.1
Because these two lines … … don’t take a parameter in the constructor, I guess that you create a context within the classes. When you load the city1… …you attach the city1 to the context in CityService. Later you add a city1 as a reference to the new Employee e1 and add e1 including this reference to city1 to the context in EmployeeService. As a result you have city1 attached to … Read more
MSSQL Error ‘The underlying provider failed on Open’
I had this error and found a few solutions: Looking at your connection string, it looks valid. I found this blog post, the problem here is that they were using Integrated Security. If you are running on IIS, your IIS user needs access to the database. If you are using Entity Framework with Transactions, Entity Framework automatically opens and … Read more
Conversion of a datetime2 data type to a datetime data type results out-of-range value
This can happen if you do not assign a value to a DateTime field when the field does not accept NULL values. That fixed it for me!
There is already an open DataReader associated with this Command which must be closed first
This can happen if you execute a query while iterating over the results from another query. It is not clear from your example where this happens because the example is not complete. One thing that can cause this is lazy loading triggered when iterating over the results of some query. This can be easily solved … Read more
EF CodeFirst: Either the parameter @objname is ambiguous or the claimed @objtype (COLUMN) is wrong
This is because of name Conflict of Class (Model) names with other reserved or generated ones, when auto creates the tables and … . Considering that EF Code First creates the intervene tables to relate 2 or more tables using name of tables for derived intervene table, so when you use a class name that employs a … Read more
EntityType has no key defined error
The Model class should be changed to :