𝗜𝗘𝗻𝘂𝗺𝗲𝗿𝗮𝗯𝗹𝗲 𝘃𝘀 𝗜𝗤𝘂𝗲𝗿𝘆𝗮𝗯𝗹𝗲 𝗶𝗻 𝗖#: 𝗗𝗶𝗳𝗳𝗲𝗿𝗲𝗻𝗰𝗲𝘀 𝗮𝗻𝗱 𝗪𝗵𝗲𝗻 𝘁𝗼 𝗨𝘀𝗲 𝗘𝗮𝗰𝗵

If you’ve worked with LINQ in C#, you’ve likely come across IEnumerable and IQueryable. While both are used to query data collections, their difference can significantly affect performance, especially when dealing with databases.

Let’s break it down and figure out when to use which, and why it matters.

IEnumerable in C#

IEnumerable is an interface used for iterating over in-memory collections in C#. When you use IEnumerable, the entire dataset is loaded into memory, and filtering or other operations are applied after the data is retrieved.

Key Points:

• Executes queries in memory (client-side).
• Belongs to the System.Collections namespace.
• Performs immediate execution.
• Suitable for in-memory data like List, Array, etc.
• Not efficient for large datasets from databases.

IQueryable in C#

IQueryable is an interface designed for querying data from external sources like databases. It translates LINQ queries into SQL and executes them on the database server, allowing filters to be applied before data is fetched.

Key Points:

• Executes queries in the database (server-side).
• Belongs to the System.Linq namespace.
• Supports deferred execution.
• Ideal for Entity Framework, LINQ to SQL, and remote queries.
• Efficient for large datasets, as filtering is done at the source.

Conclusion

Choosing between IEnumerable and IQueryable depends on where your data comes from and how you intend to process it. While both support LINQ queries, their execution behavior and performance impact differ significantly.

Key Points:

• Use IEnumerable for working with in-memory data collections.
• Use IQueryable when querying data from external sources like databases.
• IQueryable provides better performance for large datasets by pushing the filtering to the database.
• Understanding the difference helps in writing efficient, optimized, and scalable code.