Client-side evaluation in Entity Framework & Query tags

Client-side evaluation in Entity Framework Core refers to the behavior of executing parts of a LINQ query on the client-side (i.e., in the application's memory) instead of generating SQL statements to be executed in the database. Client-side evaluation occurs when a query cannot be fully translated to SQL and executed in the database. In general, client-side evaluation should be avoided whenever possible, as it can result in significant performance degradation, especially when dealing with large datasets. This is because the data must be retrieved from the database and transferred to the application's memory before the query can be executed, which can be a slow and resource-intensive process.

to prevent unintentional client-side evaluation in Entity Framework Core, the framework will throw an exception if it encounters a query that cannot be translated to SQL. However, there are some cases where client-side evaluation may be necessary or desirable, such as when working with non-primitive types or when using certain methods that are not supported by the database.to force a query to be evaluated on the client-side, you can use the AsEnumerable or ToList methods. These methods will execute the query and return an in-memory collection of objects that can be further manipulated with LINQ like this query

var customers = context.Customers
    .Where(c => c.City == "London")
    .AsEnumerable()
    .OrderBy(c => c.LastName)
    .ToList();        

how to identify which queries are executed in the database, Query tags can be useful when you're profiling or debugging your application, as they allow you to easily identify which SQL statements were generated by Entity Framework Core for a particular query. You can typically find query tags in the profiler or diagnostic tool you're using to monitor your database activity so what are the query tags in ef core? Query tags in Entity Framework Core are a way to associate a tag with a query so that you can easily identify which queries are executed in the database when profiling or debugging your application.

To add a query tag to a query in Entity Framework Core, you can use the TagWith extension method. Here's an example:

var customers = context.Customers
    .Where(c => c.City == "London")
    .TagWith("GetLondonCustomers")
    .ToList();        

and what are the penitents of using Query tags?

The main benefits of using query tags in Entity Framework Core are:

1. Query profiling: Query tags allow you to easily identify which SQL statements were generated by Entity Framework Core for a particular query. This can be useful when you're profiling your application to identify slow-running queries or to optimize the performance of your database queries.
2. Debugging: Query tags can also be useful when debugging your application, as they allow you to easily identify which queries are being executed in the database. This can be especially helpful when you're working with complex or nested queries, as it can be difficult to trace the execution path of a query without tags.
3. Documentation: Query tags can also serve as a form of documentation for your code. By adding descriptive tags to your queries, you can help other developers understand the purpose and intent of your queries, which can make it easier for them to maintain and modify your code in the future.

and you can include multiple tags in a single query by calling TagWith multiple times:

var customers = context.Customers
    .Where(c => c.City == "London")
    .TagWith("GetLondonCustomers")
    .TagWith("OnlyActiveCustomers")
    .ToList();