C# and MongoDb tips – Part 4

Modifying a cursor

The Find method doesn’t immediately return the actual results of a query. Instead they return a cursor (MongoCursor) that can be enumerated to retrieve the results of the query. The query is sent to the server when we first try to retrieve the result. This feature allows the user to control the results of the query before fetching the results by modifying the cursor.

For e.g. you can use the skip, limit, sort properties to modify the cursor. You can also use the fluent interface methods for the properties to modify the cursor. After setting these properties, you can enumerate the results to get the actual output.

[TestMethod]

public void SkipAndLimitShouldReturnPagedDataFromACursor()

{

    var database = GetDatabaseInstance();

    var collectionSettings = database.CreateCollectionSettings<Employee>("Employees");

    collectionSettings.SlaveOk = true;

    var employees = database.GetCollection(collectionSettings);

    var employeeCursor = employees.FindAll();

    employeeCursor.Skip = 5;

    employeeCursor.Limit = 2;

    Assert.IsTrue(employeeCursor.ToList().Count == 2);

}

[TestMethod]

public void SkipAndLimitUsingFluentInterfacesShouldReturnPagedDataFromACursor()

{

    var database = GetDatabaseInstance();

    var collectionSettings = database.CreateCollectionSettings<Employee>("Employees");

    collectionSettings.SlaveOk = true;

    var employees = database.GetCollection(collectionSettings);

    var employeeCursor = employees.FindAll().SetSkip(5).SetLimit(2).SetSortOrder("FirstName", "LastName");

    Assert.IsTrue(employeeCursor.ToList().Count == 2);

}