SQL Server (and Npgsql) can only cache a certain number of SQLs at some point, they have to get rid of old entries to avoid using too much memory. In addition, EF itself has an internal SQL cache for its queries, and this SQL variance makes caching impossible, leading to further EF overhead for each and every query.īut crucially, the negative performance impact of constantly varying SQLs goes beyond this particular query. This is vital for good performance: SQL Server caches SQL, performing expensive query planning only the first time a particular SQL is seen (a similar SQL cache is implemented in the database driver for PostgreSQL). This has the unfortunate consequence that the SQL produced by EF varies for different array contents – a pretty abnormal situation! Usually, when you run the same LINQ query over and over again – changing only parameter values – EF sends the exact same SQL to the database. NET variables in EF LINQ queries usually become SQL parameters, in this particular case the variable has disappeared, and its contents have been inserted directly into the SQL. īut wait, this looks suspiciously familiar – it’s the inline collection translation we saw above! And indeed, since we couldn’t parameterize the array, we simply embedded its values – as constants – into the SQL query. Up to now, all versions of EF have provided the following translation: SELECT. But what can we do for other databases, where this does not exist? Leveraging this, we pass the array of blog names as a SQL parameter directly to ANY – that’s – and get the perfect translation. WHERE b."Name" = ANY is very similar to the inline collection translation above with IN, but uses the PostgreSQL-specific ANY construct, which can accept an array type. Where(b => new (DbType = Object)], CommandType='Text', CommandTimeout='30'] You could use the following LINQ query to do so: var blogs = await context.Blogs Starting from something simple, imagine you have a bunch of Blogs, and want to query out two Blogs whose names you know. Let’s examine such a case, which also happens to be related to a highly-voted EF performance issue. In EF’s quest to translate more and more LINQ queries to SQL, we sometimes encounter odd and problematic corner cases. Let’s dive in! Translating LINQ Contains with an inline collection The fourth preview version of EF Core 8.0 preview4 includes some exciting new capabilities in query translation, as well as an important performance optimization. NET 8 as a long-term support (LTS) release. NET 8 as we near release.ĮF8 will align with. NET 6, and can therefore be used with either. These data casters are implemented by supporting dialects in order toĪssure that comparisons to the above types will work as expected, suchĭata_table.c.data.as_integer() = 5ĭata_table.c.data.The fourth preview of Entity Framework Core (EF Core) 8 is available on NuGet today! Basic informationĮF Core 8, or just EF8, is the successor to EF Core 7, and is scheduled for release in November 2023, at the same time as. In order to provide access to these elements in aīackend-agnostic way, a series of data casters are provided: Comparator.as_string() - return the element as a stringĬomparator.as_boolean() - return the element as a booleanĬomparator.as_float() - return the element as a floatĬomparator.as_integer() - return the element as an integer However, it is likely more common that an index operation isĮxpected to return a specific scalar element, such as a string or That further JSON-oriented instructions may be called upon the result Return an expression object whose type defaults to JSON by default, so Using the Python bracket operator as in some_column, those invoked by calling upon the expression I have some GeoJSON in a JSON (not JSONB) type column and none of the existing solutions worked, but as it turns out, in version 1.3.11 some new data casters were added, so now you can: records = db_session.query(Resource).filter(_string() = "Doe").all()
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