protected override void OnModelCreating(ModelBuilder modelBuilder)
	base.OnModelCreating(modelBuilder);
	modelBuilder.Entity<Document>().Property(e => e.TableOfContents) // TableOfContents is a List<TableOfContents> complex object
		.HasColumnType("jsonb")
		.HasConversion(
			v => JsonConvert.SerializeObject(v,
				new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore }),
			v => JsonConvert.DeserializeObject<List<TableOfContents>>(v,
				new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore }));
Error Message

PostgresException: 42804: column "table_of_contents" is of type json but expression is of type text
I've tried using but it doesn't appear to make a difference (assuming I set it up correctly)

https://www.npgsql.org/doc/types/jsonnet.html
Any thoughts?
          
This is in a seed method during DB initialization.
Just doing AddRangeAsync from a Deserialized JSON document await _context.Document.AddRangeAsync(documents);
var sampleDocsPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "sample-documents.json");
                var json = File.ReadAllText(sampleDocsPath);
                var documents = JsonConvert.DeserializeObject<IEnumerable<Document>>(json);
                if (documents is null || !documents.Any())
                    throw new Exception("Failed to seed with sample documents");
                    await _context.Document.AddRangeAsync(documents);
                    await _context.SaveChangesAsync();
          
@jsheely could you help out reproduce this? The below code seems to work fine, doing both types of seeding and a query. A simple self-contained code sample would be best, and since preview8 is about to come out it would be great if this could be quick :)
class Program
    static void Main(string[] args)
        using (var ctx = new BlogContext())
            ctx.Database.EnsureDeleted();
            ctx.Database.EnsureCreated();
            ctx.Blogs.Add(new Blog { Name = "WAT", Json = @"{ ""a"" : 1 }" });
            ctx.SaveChanges();
        using (var ctx = new BlogContext())
            var x = ctx.Blogs.Where(b => b.Json == @"{ ""a"" : 1 }").ToList();
public class BlogContext : DbContext
    public DbSet<Blog> Blogs { get; set; }
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        optionsBuilder.UseNpgsql("Host=localhost;Database=test;Username=npgsql_tests;Password=npgsql_tests");
    protected override void OnModelCreating(ModelBuilder modelBuilder)
        modelBuilder.Entity<Blog>().ToTable("blog")
            .Property(b => b.Json).HasColumnType("jsonb").IsRequired();
        modelBuilder.Entity<Blog>().HasData(new Blog { Id = -1, Name = "WAT", Json = @"{ ""a"" : 1 }" });
public class Blog
    public int Id { get; set; }
    public string Name { get; set; }
    public string Json { get; set; }
          
Okay great. I'll take a look. Though the one thing I notice right from the onset is that Blog.Json is of type string where in my case our json is List.
Stored in the DB is a json array. Will see if that makes any difference.
          
I did confirm that yours does work for me with the string. It seems specific to the IList
Here is a repo where it works in 2.2.6 of EF Core and breaks in preview7
https://github.com/jsheely/ef-core-json

https://github.com/jsheely/ef-core-json/tree/preview7
Only difference between the two branches is the packages
          
Doing a little more testing though it's interesting that it works with HasData(). It seems that only ctx.SaveChanges() breaks it.
I also can confirm that it can read the data just fine.

var x = ctx.Blogs.Where(b => b.Id == -1).ToList();