Microsoft Certified Solutions Developer (MCSD) Certification Practice Test

What is the way to perform an outer join using LINQ?

1. Using Join and DefaultIfEmpty

2. Using SelectMany and GroupBy

3. Using Join and GroupBy

4. Using Merge and DefaultIfEmpty

The correct answer is: Using Join and DefaultIfEmpty

An outer join in LINQ can be performed by combining the Join method with DefaultIfEmpty. This approach allows you to retrieve all records from one sequence and the matching records from another sequence, filling in with default values for those records that do not have a match. This effectively simulates the behavior of an outer join, where you want to include all entries from one side of the join regardless of whether they have corresponding entries in the other side. The use of Join by itself would only return matching records, which does not satisfy the requirements of an outer join. Conversely, while SelectMany and GroupBy might help in manipulating data sets, they do not directly facilitate the outer join operation. Similarly, using Merge is not a method in LINQ, making any option with it invalid for performing outer joins. Thus, the combination of Join with DefaultIfEmpty is the correct method for achieving an outer join in LINQ.