C#: what's the difference between IEnumerable and IQueryable in EF Core?
asked 4 months ago213 viewsen
My query loads the entire Orders table into memory before filtering, even though I wrote .Where(). The code passes the DbSet through a method that takes IEnumerable<Order>.
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1 Answer
That's exactly the problem:
- IQueryable<T> builds an expression tree. EF translates .Where, .OrderBy and .Take to SQL and runs it in the database. - IEnumerable<T>: once the query is typed as this, subsequent LINQ runs in memory (LINQ to Objects). EF runs SELECT * FROM Orders and filters in C#.
// ❌ filters in memory
IEnumerable<Order> Recent(IEnumerable<Order> src) => src.Where(o => o.Date > cutoff);
// ✅ filters in SQL
IQueryable<Order> Recent(IQueryable<Order> src) => src.Where(o => o.Date > cutoff);Keep queries as IQueryable until the final ToListAsync(). To see the generated SQL, log it (optionsBuilder.LogTo(Console.WriteLine)) or call query.ToQueryString().
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