Id value not retrieved when multi-column PK

[mauriciomagni]

Description

When a record is inserted in a table that has a multi-column primary key, the Identity value generated is not retrieved.

Repro steps

1. Create a silly table:

create table SillyTable (TenantId int not null, Id int identity not null)
alter table SillyTable add constraint PK_SillyTable primary key (TenantId, Id)

2. Insert a row and get the value for Id

let testError () =
        let ctx = sql.GetDataContext()
        let row = ctx.Dbo.SillyTable.Create()
        row.TenantId <- 1
        ctx.SubmitUpdates()
        let id = row.Id //always 0
        let readRow = ctx.Dbo.SillyTable |> Seq.last
        let readId = readRow.Id //return just inserted value (identity)
        (id, readId) //readId has the expected value

Expected behavior

After SubmitUpdates(), the row.Id value should be updated with the value generated by the DB.

Actual behavior

The Id column keeps its default value (0 in this case) after SubmitUpdates()

Known workarounds

None

Related information

Operating System: Windows 10 Pro
Visual Studio: 2017 15.8.1
FSharp.Core 4.5.2
SqlProvider 1.1.48
DB: SqlLocalDB v13