Enumerable vs ToList: Choosing the Right Method for Query Execution in EF Core

  • Enumerable: This method is used to switch from querying the database to performing operations on the resulting in-memory collection. This is useful when you want to perform complex data manipulations that cannot be easily translated to SQL. Note that when you use Enumerable, all data is retrieved from the database before the operations are performed, which can have performance implications for large data sets.

  • ToList: This method is used to execute the query and return the results as a list. It is used to materialize the results of a query into a collection in memory. Once the query is executed and the results are materialized, you can perform operations on the collection. This method can be more efficient than using Enumerable because it retrieves only the necessary data from the database and materializes it into a list.

Here's an example of using Enumerable:

var orders = dbContext.Orders
    .Where(o => o.CustomerId == customerId)
    .AsEnumerable()
    .Where(o => o.OrderDate.Year == year)
    .ToList();

In this example, we're using Where to filter the orders by CustomerId, then using AsEnumerable to switch to in-memory operations, and finally using Where to filter the orders by OrderDate.Year. The ToList method is used to execute the query and return the results as a list.

And here's an example of using ToList:

var orders = dbContext.Orders
    .Where(o => o.CustomerId == customerId && o.OrderDate.Year == year)
    .ToList();

In this example, we're using Where to filter the orders by both CustomerId and OrderDate.Year. The ToList method is used to execute the query and return the results as a list.

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