Using JSON_QUERY as DbFunction in EF Core 6 - json

Question

I am attempting to utilize SQL Server's built in JSON functionality with Entity Framework Core 6. It actually works exceedingly well with JSON_VALUE as shown below.
var results = _context.Pages.Where(p => MyDbFunctions.JsonValue(p._PublishedContent, "$.content").ToLower().Contains("test"));
DbContext is as follows:
public class JsonValueTestingContext : DbContext
{
public JsonValueTestingContext(DbContextOptions context) : base(context) { }
public DbSet<Page> Pages { get; set; }
public DbSet<Template> Templates { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.HasDbFunction(() => MyDbFunctions.JsonValue(default(string), default(string)));
modelBuilder.HasDbFunction(() => MyDbFunctions.JsonQuery(default(string), default(string)));
}
}
public static class MyDbFunctions
{
[DbFunction("JSON_VALUE", Schema = "", IsBuiltIn = true)]
public static string JsonValue(string source, [NotParameterized] string path) => throw new NotSupportedException();
[DbFunction("JSON_QUERY", Schema = "", IsBuiltIn = true)]
public static string JsonQuery(string source, [NotParameterized] string path) => throw new NotSupportedException();
}
The challenge I'm running into is that JSON_VALUE is good for basic types like string, int, boolean, datetime, etc. However, I do also store a string of arrays like ['Apple', 'Orange', 'Pear'] and I would very much like to do something similar to the following:
var results = _context.Pages.Where(p => MyDbFunctions.JsonQuery(p._PublishedContent, "$.content").Contains("Apple"));
I can't seem to figure out how to achieve the latter. If I try to return a string[] type for JSON_QUERY in MyDbFunctions, it says it is an invalid return type for the provider. I've tried all sorts of casting too, and Linq cannot translate. I feel like there must be a way.

Answer 1

The answer is to use OPENJSON, not JSON_QUERY in this scenario. On top of that there are some additional considerations. For example, you need to create a Keyless object with Key / Value attributes and specify IQueryable as the return type on the OPENJSON static method. See example below.
public class JsonValueTestingContext : DbContext
{
public JsonValueTestingContext(DbContextOptions context) : base(context) { }
public DbSet<Page> Pages { get; set; }
public DbSet<Template> Templates { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.HasDbFunction(() => MyDbFunctions.JsonValue(default(string), default(string)));
modelBuilder.HasDbFunction(() => MyDbFunctions.OpenJson(default(string), default(string)));
}
}
public static class MyDbFunctions
{
[DbFunction("JSON_VALUE", Schema = "", IsBuiltIn = true)]
public static string JsonValue(string source, [NotParameterized] string path) => throw new NotSupportedException();
[DbFunction("OPENJSON", Schema = "", IsBuiltIn = true)]
public static IQueryable<ArrayDatabaseItem> OpenJson(string source, [NotParameterized] string path) => throw new NotSupportedException();
}
[Keyless]
public class ArrayDatabaseItem
{
public int Key { get; set; }
public string Value { get; set; }
}
And usage may look like:
var results = _context.Pages.Where(p => MyDbFunctions.OpenJson(p._PublishedContent, "$.array_item").Any(c => c.Value == "Choice 2"));
#Charlieface's comment and this part of Microsoft Docs helped me arrive at the answer.