Incorrect IsDBNull results on null rowversion when using ReadAsync

[roji]

When calling IsDBNull on a rowversion column after having called ReadAsync, false is return for a null value instead of true. This occurs on Microsoft.Data.SqlClient 3.0, and is likely related to #998 (/cc @Wraith2).

The below minimal repro uses a left join to produce a null rowversion. This was originally raised and repro'd on EF Core by @frankbuckley in dotnet/efcore#25074, thanks.

Repro

await using var conn = new SqlConnection("Server=localhost;Database=test;User=SA;Password=Abcd5678;Connect Timeout=60;ConnectRetryCount=0");
await conn.OpenAsync();

await using var cmd = new SqlCommand(@"
DROP TABLE IF EXISTS [Price];
DROP TABLE IF EXISTS [Occurrences];

CREATE TABLE [Occurrences] (
    [Id] int NOT NULL IDENTITY,
    CONSTRAINT [PK_Occurrences] PRIMARY KEY ([Id])
);

CREATE TABLE [Price] (
    [Id] int NOT NULL IDENTITY,
    [Timestamp] rowversion NOT NULL,
    [OccurrenceId] int NOT NULL,
    [Value] decimal(18,2) NOT NULL,
    CONSTRAINT [PK_Price] PRIMARY KEY ([Id]),
    CONSTRAINT [FK_Price_Occurrences_OccurrenceId] FOREIGN KEY ([OccurrenceId]) REFERENCES [Occurrences] ([Id]) ON DELETE CASCADE
);

INSERT INTO [Occurrences] DEFAULT VALUES;
INSERT INTO [Occurrences] DEFAULT VALUES;", conn);

await cmd.ExecuteNonQueryAsync();

cmd.CommandText = @"
SELECT [o].[Id], [p].[Id], [p].[OccurrenceId], [p].[Timestamp], [p].[Value]
FROM [Occurrences] AS [o]
LEFT JOIN [Price] AS [p] ON [o].[Id] = [p].[OccurrenceId]
ORDER BY [o].[Id]";

await using var reader = await cmd.ExecuteReaderAsync();

// Read one row with Read - works fine
reader.Read();
Console.WriteLine($"IsDBNull after Read: {reader.IsDBNull(3)}");

// Read another row with ReadAsync - bug
await reader.ReadAsync();
Console.WriteLine($"IsDBNull after ReadAsync: {reader.IsDBNull(3)}");
_ = reader.GetFieldValue<byte[]>(3); // Throws

[cheenamalhotra]

Hi @roji

This issue has been fixed by PR #1182 and will be included in 4.0.0-preview1 release.

One thing to note:
_ = reader.GetFieldValue<byte[]>(3); // Throws will now throw below exception:

SqlNullValueException: Data is Null. This method or property cannot be called on Null values.

as we can't support cast on DBNull.

_ = reader.GetFieldValue<DBNull>(3); will be supported.

[roji]

Thanks @cheenamalhotra, good to now!

Yes, it's definitely expected that GetFieldValue throw if IsDBNull returns false true, no problem there.

[roji]

Duplicate of #1175

[cheenamalhotra]

Yes, it's definitely expected that GetFieldValue throw if IsDBNull returns false, no problem there.

if IsDBNull returns 'true' :)

[roji]

Yes :)

[roji]

Just to confirm that the above indeed behaves correctly on 4.0.0-preview1 (IsDBNull return true after ReadAsync)