What is model column in MigrationHistory table?

Question

In EF6 when you use Code First Migration, it creates a table that called __MigrationHistory with four column:

MigrationId
ContextKey
Model
ProductVersion

What is the binary data in Model field? Does it contain database schema? I mean if I have a database with hundreds of tables, does the Model field contain all of them?

Answer 1

On MSSQL use

SELECT *, CONVERT(xml, DECOMPRESS(Model)) FROM [dbo].[__MigrationHistory]

Answer 2

Internally it uses this function to get value for Model field:

    public virtual byte[] Compress(XDocument model)
    {
        DebugCheck.NotNull(model);

        using (var outStream = new MemoryStream())
        {
            using (var gzipStream = new GZipStream(outStream, CompressionMode.Compress))
            {
                model.Save(gzipStream);
            }

            return outStream.ToArray();
        }
    }

So yes, it seems that the field contains whole model in a compressed form.

Answer 3

For the sake of EF's migration process understanding I would suggest checking Max Vasilyev's enlightening Inside of Entity Framework Migrations or How to View Generated Xml-Schema article .

The article provides a sample project. You just need to save one of the sample outputs to .edmx file e open it using Visual Studio.