在 EF Core 6 中使用原始 SQL

Question

I am currently trying to find different areas where Linq is not sufficient and FromSqlRaw or ExecuteSqlRaw have to be used.

Some examples I have found are

• Bulk updates https://learn.microsoft.com/en-us/ef/core/performance/efficient-updating
• Executing stored procedures https://learn.microsoft.com/en-us/ef/core/querying/raw-sql

However I am looking for more areas where Linq does not perform good enough and even queries that cannot be generated from Linq in EF Core when it comes to database access.

My goal is to find poor performing Linq translations and examine the cause.

Answer 1

This is a bit of a solution looking for a problem. Given an application and looking for inefficiencies that might benefit from a different approach is something I would start off using a profiler and observing the database access in as close to a production capacity as I am allowed to get.

EF is like any tool, it can be leveraged to create works of art, and it can be abused and misused to create shanties. Even when done correctly, optimizations like indexes are something that are tuned based on looking at real-world options. There are many options that I would look at to address performance issues before considering direct to SQL. Typical culprits that can be easily identified via profiling:

1. Lazy loading. (Dozens to hundreds of queries following up a "main" query.)
2. Over-use of eager loading. (Queries involving a heck of a lot of joins)
3. Sloppy use of client-side evaluation. (Either enabling that feature in EF Core, or slapping a ToList somewhere when a query complains to "fix" it, AsSplitQuery can help here, Projection is a better solution in most cases)
4. Lack of pagination where more data is returned than necessary. (Similar to #3, having methods like "GetAll" and then applying filtering, pagination, etc.)
5. Giving users too much flexibility in querying that they don't need 99% of the time, but in that 1% someone does try it, grinds the system to a halt. (Giving users filters/sorts on ALL columns and performing things like string.Contains by default for text searches)
6. Giving users access to expensive, but necessary queries in real-time. (Big, justified queries, but being run against the production dataset and not "throttled" by something like a Queue to ensure too many of these monsters don't get run at once.)

Those are some of the top culprits that come to mind around performance, and none of them resort to going to SQL. Batch processing in your list is certainly one case that I believe does deserve looking outside of Linq, and potentially outside of EF all-together. Stored Procs I am mixed on. If there is business logic that is shared between an EF-supported application and another existing system and I want to share that business logic as-is. The trouble is that if I'm relying on the Sproc for business rules then there's little point to EF, and if I'm splitting business rules between C#/EF and Sprocs, then that's having to manage logic in two locations.