Why is the DBSet Add failing, and also destroying the existing Customer entries in the DBSet? - entity-framework

Question

Our programming involves some Mock testing using In Memory Data.
// Let us create some in-memory data
// Create a list of Customer
List<Customer> listOfCustomers = new List<BlahProjectBlahExample.Domain.Objects.Customer>()
{ new Customer { CustomerID = "1 ", CompanyName = "Chicago Bulls", ContactName = "Michael Jordan", ContactTitle = "top basket ball player", Address = "332 testing lane", City = "Chicago", Region = "Illinois", PostalCode = "484894", Country = "USA", Phone = "3293993", Fax = "39393" },
new Customer { CustomerID = "2 ", CompanyName = "Miami Heat", ContactName = "Lebron James", ContactTitle = "second best basket ball player", Address = "90 test street", City = "Miami", Region = "Florida", PostalCode = "4869394", Country = "USA", Phone = "3293213", Fax = "33393" },
new Customer { CustomerID = "3 ", CompanyName = "Oklahoma City Thunder", ContactName = "Kevin Durant", ContactTitle = "current top basket ball player", Address = "35 test row", City = "Oklahoma City", Region = "Oklahoma", PostalCode = "480290", Country = "USA", Phone = "304923", Fax = "33325" }
};
// Convert the list to an IQueryable list
IQueryable<Customer> queryableListOfCustomerInMemoryData = listOfCustomers.AsQueryable();
// Let us create a Mocked DbSet object.
Mock<DbSet<BlahProjectBlahExample.Domain.Objects.Customer>> mockDbSet = new Mock<DbSet<BlahProjectBlahExample.Domain.Objects.Customer>>();
// Force DbSet to return the IQueryable members
// of our converted list object as its
// data source
mockDbSet.As<IQueryable<BlahProjectBlahExample.Domain.Objects.Customer>>().Setup(m => m.Provider).Returns(queryableListOfCustomerInMemoryData.Provider);
mockDbSet.As<IQueryable<BlahProjectBlahExample.Domain.Objects.Customer>>().Setup(m => m.Expression).Returns(queryableListOfCustomerInMemoryData.Expression);
mockDbSet.As<IQueryable<BlahProjectBlahExample.Domain.Objects.Customer>>().Setup(m => m.ElementType).Returns(queryableListOfCustomerInMemoryData.ElementType);
mockDbSet.As<IQueryable<BlahProjectBlahExample.Domain.Objects.Customer>>().Setup(m => m.GetEnumerator()).Returns(queryableListOfCustomerInMemoryData.GetEnumerator());
Mock<BlahProjectBlahDataContext> mockedReptryCtxt = new Mock<BlahProjectBlahDataContext>();
mockedReptryCtxt.Setup(q => q.Customers).Returns(mockDbSet.Object);
mockedReptryCtxt.Setup(q => q.Set<Customer>()).Returns(mockDbSet.Object);
mockedReptryCtxt.CallBase = true;
DbSet<Customer> inMemoryDbSetCustomer = mockedReptryCtxt.Object.Set<Customer>();
In the following code, I used a loop to see the contents of the inMemoryDbSetCustomer, and it contained the expected data.
Customer something;
foreach (var entry in inMemoryDbSetCustomer)
{
something = entry as Customer;
}
Sadly, when I try to add a new customer,
1) the inMemoryDbSetCustomer fails to add the customer
2) the inMemoryDbSetCustomer.Add(someCust) returns NULL
3) the inMemoryDbSetCustomer seems to have lost all it's other Customer entries.
Customer someCust = new Customer { CustomerID = "4 ", CompanyName = "Kolkota Knights", ContactName = "Sachin Tendulkar", ContactTitle = "current top cricket player", Address = "35 test row", City = "Kolkota", Region = "West Bengal", PostalCode = "3454534", Country = "India", Phone = "304923", Fax = "33325" };
try
{
Customer returnCust = (Customer)(inMemoryDbSetCustomer.Add(someCust));
}
catch(Exception ex ){
}
Why is the DBSet Add failing, and also destroying the existing Customer entries in the DBSet?
Update With Answer
Thanks to #Werlang suggestion. The following code addition helped:
mockDbSet.Setup(m => m.Add(It.IsAny<Customer>()))
.Callback<Customer>((Customer c) => { listOfCustomers.Add(c); })
.Returns((Customer c) => c);
Also, if you mocking DBSets with Moq Framework like I am then the following stackoverflow posting will be helpful because you might face a similar problem:
What steps to get rid of Collection was modified; enumeration operation may not execute. Error?

Answer 1

You've mocked the queryable to return a fixed set of data, when accessed via IQueryable. But Add's are maintained in a separated list on DbContext internal in the form of DbEntry's.
I suggest you to mock the Add() method too, addind the new element to mocked array (listOfCustomers).