问题
Our programming involves some Mock testing using In-Memory Data. Therefore, we implemented the following code that would first create In-Memory Data of Customer objects
// Let us create some in-memory data
// Create a list of Customer
List<Customer> listOfCustomers = new List<BlahBlahExample.Domain.Objects.Customer>()
{ new Customer { CustomerID = "1 ",Orders = new HashSet<Order>(), CustomerDemographics = new HashSet<CustomerDemographic>(), 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 ",Orders = new HashSet<Order>(),CustomerDemographics = new HashSet<CustomerDemographic>() , 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 ",Orders = new HashSet<Order>(),CustomerDemographics = new HashSet<CustomerDemographic>() , 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<BlahBlahExample.Domain.Objects.Customer>> mockDbSet = new Mock<DbSet<BlahBlahExample.Domain.Objects.Customer>>();
// Force DbSet to return the IQueryable members
// of our converted list object as its
// data source
mockDbSet.As<IQueryable<BlahBlahExample.Domain.Objects.Customer>>().Setup(m => m.Provider).Returns(queryableListOfCustomerInMemoryData.Provider);
mockDbSet.As<IQueryable<BlahBlahExample.Domain.Objects.Customer>>().Setup(m => m.Expression).Returns(queryableListOfCustomerInMemoryData.Expression);
mockDbSet.As<IQueryable<BlahBlahExample.Domain.Objects.Customer>>().Setup(m => m.ElementType).Returns(queryableListOfCustomerInMemoryData.ElementType);
mockDbSet.As<IQueryable<BlahBlahExample.Domain.Objects.Customer>>().Setup(m => m.GetEnumerator()).Returns(queryableListOfCustomerInMemoryData.GetEnumerator());
mockDbSet.Setup(m => m.Add(It.IsAny<Customer>())).Callback<Customer>(listOfCustomers.Add);
Mock<BlahBlahAuditMappingProvider> jsAudtMppngPrvdr = new Mock<BlahBlahAuditMappingProvider>();
Mock<BlahBlahDataContext> fctry = new Mock<BlahBlahDataContext>(jsAudtMppngPrvdr.Object);
Mock<BlahBlahDataContext> qryCtxt = new Mock<BlahBlahDataContext>();
Mock<BlahBlahAuditContext> audtCtxt = new Mock<BlahBlahAuditContext>();
Mock<BlahBlahDataContext> mockedReptryCtxt = new Mock<BlahBlahDataContext>();
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 next excerpt of code( which is our "Code Under Test"), I add a new Customer to the existing In-Memory Data, and then Invoke SaveChanges on the Mocked Object.
Customer returnCust = (Customer)(mockedReptryCtxt.Object.Set<Customer>().Add(new Customer { CustomerID = "4 ", Orders = new HashSet<Order>(), CustomerDemographics = new HashSet<CustomerDemographic>(), 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" }));
mockedReptryCtxt.Object.SaveChanges();
Later on in the code, I have the following excerpt of code where _context.Set() will return the In-Memory Data DBSet that we created previously
var query = _context.Set<TEntity>().AsQueryable();
if (typeof(TEntity).Name.Contains("Audit"))
{
return query;
}
if (includes != null && includes.Any())
{
foreach (var include in includes)
{
query = query.Include(include);
}
}
List<TEntity> resultsAsList = query.ToList(); // Error Thrown When using ToList()
var results = resultsAsList.AsQueryable();
When we invoke ToList(), it Throws the following Error:
System.InvalidOperationException was unhandled by user code
HResult=-2146233079
Message=Collection was modified; enumeration operation may not execute.
Source=mscorlib
StackTrace:
at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
at System.Collections.Generic.List`1.Enumerator.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at BlahBlah.Framework.EntityFramework.EntityFrameworkRepository`1.ConcreteQuery(List`1 includes) in d:\EMIS\BlahBlah Framework\BlahBlahFrameworkLightweight\BlahBlah.Framework.EntityFramework\EntityFrameworkRepository.c s:line 51
at Castle.Proxies.EntityFrameworkRepository`1Proxy.ConcreteQuery_callback(List`1 includes)
at Castle.Proxies.Invocations.EntityFrameworkRepository`1_ConcreteQuery.InvokeMethodOnTarget()
at Castle.DynamicProxy.AbstractInvocation.Proceed()
at Moq.Proxy.CastleProxyFactory.CallContext.InvokeBase()
at Moq.InvokeBase.HandleIntercept(ICallContext invocation, InterceptorContext ctx, CurrentInterceptContext localctx)
at Moq.Interceptor.Intercept(ICallContext invocation)
at Moq.Proxy.CastleProxyFactory.Interceptor.Intercept(IInvocation invocation)
at Castle.DynamicProxy.AbstractInvocation.Proceed()
at Castle.Proxies.EntityFrameworkRepository`1Proxy.ConcreteQuery(List`1 includes)
at BlahBlah.Framework.Core.Repository.BaseRepository`1.Query(List`1 includes) in d:\EMIS\BlahBlah Framework\BlahBlahFrameworkLightweight\BlahBlah.Framework.Core\Repository\BaseRepository.cs:line 149
at Castle.Proxies.EntityFrameworkRepository`1Proxy.Query_callback(List`1 includes)
at Castle.Proxies.Invocations.IRepository`1_Query.InvokeMethodOnTarget()
at Castle.DynamicProxy.AbstractInvocation.Proceed()
at Moq.Proxy.CastleProxyFactory.CallContext.InvokeBase()
at Moq.InvokeBase.HandleIntercept(ICallContext invocation, InterceptorContext ctx, CurrentInterceptContext localctx)
at Moq.Interceptor.Intercept(ICallContext invocation)
at Moq.Proxy.CastleProxyFactory.Interceptor.Intercept(IInvocation invocation)
at Castle.DynamicProxy.AbstractInvocation.Proceed()
at Castle.Proxies.EntityFrameworkRepository`1Proxy.Query(List`1 includes)
at BlahBlah.Test.Unit.CntrlrsTests.CustomerControllerTest.Test_Creation_Of_Customer_Using_Constructor_Of _Customer_Controller_That_Expects_Arguments() in d:\EMIS\BlahBlah Framework\BlahBlahFrameworkLightweight\BlahBlah.Test.Unit\CntrlrsTests\CustomerControllerTest.cs:line 278
InnerException:
What steps do we need to take in order to stop the said error from being thrown( preferably without Changing too much of our Code Under Test)?
回答1:
I had this problem as well but not iterating over the collection isn't really an option for me. After some thought, I did figure out a solution. The issue is that the mock sets up the various IQueryable properties off of a fixed IQueryable object from the original list. That causes any modification of that list to invalidate the corresponding IQueryable. The solution is to get a new IQueryable on each access using a lambda with Moq.
Here's the helper function I created to make mocking out DBSets easier, using the described technique.
public static Mock<DbSet<T>> MockDbSet<T>(List<T> list) where T : class
{
var mockSet = new Mock<DbSet<T>>();
mockSet.As<IQueryable<T>>().Setup(m => m.Provider).Returns(() => list.AsQueryable().Provider);
mockSet.As<IQueryable<T>>().Setup(m => m.Expression).Returns(() => list.AsQueryable().Expression);
mockSet.As<IQueryable<T>>().Setup(m => m.ElementType).Returns(() => list.AsQueryable().ElementType);
mockSet.As<IQueryable<T>>().Setup(m => m.GetEnumerator()).Returns(() => list.GetEnumerator());
mockSet.Setup(m => m.Add(It.IsAny<T>())).Callback((T x) => list.Add(x));
mockSet.Setup(m => m.AddRange(It.IsAny<IEnumerable<T>>())).Callback((IEnumerable<T> x) => list.AddRange(x));
mockSet.Setup(m => m.Remove(It.IsAny<T>())).Callback((T x) => list.Remove(x));
mockSet.Setup(m => m.RemoveRange(It.IsAny<IEnumerable<T>>())).Callback((IEnumerable<T> x) => list.RemoveAll(x.Contains));
return mockSet;
}
Edit: Added AddRange, Remove, RemoveRange since why not...
Edit 2: Correction for RemoveRange
回答2:
I found a really Clumsy Solution:
List<TEntity> tempList = new List<TEntity>();
for (int i = query.Count() - 1; i >= 0; i--)
{
tempList.Add(query.ElementAt(i));
}
List<TEntity> resultsAsList = tempList.ToList();
var results = resultsAsList.AsQueryable();
In the aforementioned code, it is important to use a for loop with an index to go through the DBSet instance. Furthermore, in the loop, you add each element to a List. ( Basically, it's important to Avoid using the Iterator)
来源：https://stackoverflow.com/questions/27009273/what-steps-to-get-rid-of-collection-was-modified-enumeration-operation-may-not