# V3078. Sorting keys priority will be reversed relative to the order of 'OrderBy' method calls. Perhaps, 'ThenBy' should be used instead.

The analyzer has detected a potential error: 'OrderBy' or 'OrderByDescending' methods are called twice in a row. The result of such sorting may differ from the expected one.

Consider an example:

    var seq = points.OrderBy(item => item.Primary)
                    .OrderBy(item => item.Secondary);

Let's say a programmer wants to sort a collection in the following way: the elements must be grouped and sorted by 'Primary', and after that, each group must be sorted by 'Secondary' inside the resulting collection.

In fact, the collection's elements will be grouped and sorted by 'Secondary', and after that, each group will be sorted by 'Primary' inside the resulting collection.

To get the expected behavior, the second 'OrderBy' call should be replaced with the 'ThenBy' call.

    var seq = points.OrderBy(item => item.Primary)
                    .ThenBy(item => item.Secondary);

To get the intended behavior, it is also possible to use two 'OrderBy' calls. To do this, we need to swap the calls:

    var seq = points.OrderBy(item => item.Secondary)
                    .OrderBy(item => item.Primary);

A programmer can make a similar error when writing code with the help of query syntax:

    var seq = from item in points
              orderby item.Primary
              orderby item.Secondary
              select item;

We can fix the code as follows:

    var seq = from item in points
              orderby item.Primary, item.Secondary
              select item;

You can look at examples of errors detected by the V3078 diagnostic.