“Experts often possess more data than judgment.” Colin Powell

“It is a capital mistake to theorize before one has data.” Arthur Conan Doyle

This is the second post in the series. To read the first episode go to Getting the Most Out of Entity Framework Core – Part 1.

I love databases! I am not a DBA, Database Developer or a Data Expert but I do love data and what it brings to the applications I develop. With that I also the data experts I work with on projects. They are my partners in crime and I use them to make the systems we develop better. I also try to make their work lives better by learning from them and doing as much as I can before I go to them for help.

In this series, we have looked at the features of Entity Framework Core that will make you a better developer. Now I want to show you how to make your relationship with your database and (if you have them) the data professionals that support your SQL Server databases.

The feature we will look at in this part of the Entity Framework Core series is Query Tags. It is a very easy feature to use in your new projects and also to refactor in existing but more important Query Tags will make your DBA’s life so much better! After you read this post please go over to my friend and PASS President Grant Fritchey’s blog post about how to work with Query Tags when passed to SQL Server.

Using Query Tags to Help Your DBA Monitor the SQL Server Database

Using Query Tags will match your Entity Framework Core query to the generated SQL SELECT statement that is passed to the SQL Server for execution. By using the
TagWith() method that was added to Entity Framework Core 2.2 the text will be added to the MSSQL logs for diagnostic and investigation purposes.

The following example shows how to work with Query Tags and the TagWith() method in your Entity Framework Core 2.2 queries.

The first thing to notice is that we pass a string to the TagWith() method that will be added to the MSSQL database logs. Here are the things to remember using the WithTag() method:

  • You can add multiple WithTag() method calls. They will cumulate and be sent to MSSQL in the order in your LINQ query.
  • You can pass a multi-line string using passing a verbatim string using the @ character,
  • You cannot use Query Tags with the Explicitly Compiled Query feature of Entity Framework Core.

The content below is what we will see in the MSSQL log files.

By adding a simple method to our Entity Framework Core 2.2 LINQ queries, we are not only passing additional information to our MSSQL databases but we are also making the lives of our team members who work on those databases better. Keep that in mind the next time you write Entity Framework Core LINQ queries in your .NET Core applications.

Remember to also read Grant Fritchey’s blog post “Combine Extended Events and TagWith to Monitor Entity Framework”.

“I think you can have a ridiculously enormous and complex data set, but if you have the right tools and methodology then it’s not a problem.” Aaron Koblin

2 thoughts on “Getting the Most Out of Entity Framework Core (Part 2) with Query Tags

  1. As a C# developer, how many times has a DBA come to you with a huge inefficient query that is getting generated from LINQ somewhere in a huge code base that has a lot of similar code in many places? It can be a significant effort to find where the LINQ is that generates this specific SQL.

    If you use .TagWith() to embed a class and method name as Chris shows in the example, this becomes trivial. saving you a lot of time when you might be under pressure to come up with a quick answer..

    Please have a look at https://github.com/aspnet/EntityFrameworkCore/issues/14134 and see if you have any ideas to contribute regarding a way to extend .TagWith to provide the class and method name by default. The Microsoft development team seems willing to do it if a robust method can be found.

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