C#: What is LINQ in C#?

LINQ (Language Integrated Query) — query syntax for data sources.

Two syntaxes:

1. Query syntax:

1var result = from x in numbers
2             where x > 5
3             select x * 2;

2. Method syntax:

1var result = numbers
2    .Where(x => x > 5)
3    .Select(x => x * 2);

LINQ providers:

• LINQ to Objects (in-memory).
• LINQ to SQL (databases).
• LINQ to XML.
• LINQ to Entities (Entity Framework).

Common operators:

• Filtering: Where, OfType.
• Projection: Select, SelectMany.
• Ordering: OrderBy, OrderByDescending, ThenBy.
• Grouping: GroupBy.
• Joining: Join, GroupJoin, SelectMany.
• Aggregation: Count, Sum, Average, Min, Max.
• Quantifiers: Any, All, Contains.
• Elements: First, Last, ElementAt, Single.
• Set: Distinct, Union, Intersect, Except.