FS0039: The namespace is not defined

Question

I'm building a Web API in F# to test some things out. I come from a C# background and I've structured things how I do there.

You can find the repo here: https://github.com/MrGodlike6/WebApiTest

I've referenced the WebApiTest.Repositories.SqlServer project in WebApiTest.WebApi but for some reason Visual studio says it can't find the WebApiTest.Repositories.SqlServer namespace.

The thing is that the solution compiles fine and I can run the application, it's just that I don't have IntelliSense for anything coming from the SqlServer project (e.g. in the CompositionRoot module).

I've tried a lot of things, from different DBs, to making a .NET Framework 4.7.2 project for the DB project. So far nothing works. Tried both Nuget & Paket and no difference. Tried VS 2019. In VS 2022 it gives some compile error that is unrelated.

I used dotPeek from JetBrains to look at the resulting .dll and the namespace & module are there as expected. Don't know what could be causing this.

Also can you indicate if the project/folder structure that I use is good for F#? Any other suggestions are also welcome.

EDIT: The SQL part is based of https://github.com/isaacabraham/get-programming-fsharp/tree/master/src/code-listings/lesson-35. Here everything works, although the SQL code is not put in a separate project.

I've commented the SqlEnumProvider and I no longer have problems in the composition root. I'll look a little closer at this provider and see if I can come up with something.

EDIT2: Created a issue on GitHub: https://github.com/fsprojects/FSharp.Data.SqlClient/issues/410

Answer 1

I've reproduced what you're seeing. The problem appears to be caused by a design-time error in the FSharp.Data type provider. In particular, SqlEnumProvider seems to be the source. When I remove the DbOperations type from AccountRepository.fs (using plain strings instead of enum values), I'm able to get Intellisense for WebApiTest.Repositories.SqlServer in CompositionRoot.fs.

Here's my kludgy workaround:

[<AutoOpen>]
module private DB =
    let [<Literal>] Conn = @"Data Source=.;Database=BankAccountDb;Integrated Security=True;Connect Timeout=60"
    type AccountsDb = SqlProgrammabilityProvider<Conn>
    type GetAccountId = SqlCommandProvider<"SELECT TOP 1 AccountId FROM dbo.Account WHERE Owner = @owner", Conn, SingleRow = true>
    type FindTransactions = SqlCommandProvider<"SELECT Timestamp, OperationId, Amount FROM dbo.AccountTransaction WHERE AccountId = @accountId", Conn>
    type FindTransactionsByOwner = SqlCommandProvider<"SELECT a.AccountId, at.Timestamp, at.OperationId, at.Amount FROM dbo.Account a LEFT JOIN dbo.AccountTransaction at on a.AccountId = at.AccountId WHERE Owner = @owner", Conn>
    // type DbOperations = SqlEnumProvider<"SELECT Description, OperationId FROM dbo.Operation", Conn>

let toBankOperation operationId =
    match operationId with
        | "Deposit" -> Deposit
        | "Withdraw" -> Withdraw
        | _ -> failwith "Unknown operation!"

let fromBankOperation bankOperation =
    match bankOperation with
        | Deposit -> "Deposit"
        | Withdraw -> "Withdraw"

I searched for an existing issue on GitHub, but didn't find one, so you might want to open a new one yourself.

If anyone else wants to try this, here's the dummy database schema I used to get things to compile:

USE [BankAccountDb]
GO
/****** Object:  Table [dbo].[Account]    Script Date: 9/16/2021 11:40:48 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Account](
    [Owner] [nchar](10) NOT NULL,
    [AccountId] [uniqueidentifier] NOT NULL
) ON [PRIMARY]
GO
/****** Object:  Table [dbo].[AccountTransaction]    Script Date: 9/16/2021 11:40:48 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[AccountTransaction](
    [AccountId] [uniqueidentifier] NOT NULL,
    [Timestamp] [datetime] NOT NULL,
    [OperationId] [nchar](10) NOT NULL,
    [Amount] [money] NOT NULL
) ON [PRIMARY]
GO
/****** Object:  Table [dbo].[Operation]    Script Date: 9/16/2021 11:40:48 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Operation](
    [Description] [nvarchar](100) NULL,
    [OperationId] [nvarchar](100) NULL
) ON [PRIMARY]
GO

Answer 2

Thank you Brian for the script.

As the documentation says,
"An enumeration type (or enum type) is a value type defined by a set of named constants of the underlying integral numeric type."
I changed the OperationId column data type to int in dbo.Operation and dbo.AccountTransaction and populated the table dbo.Operation, because the SqlEnumProvider complained about lack of data during the compilation.

CREATE TABLE [dbo].[Operation] (
    [Description] NVARCHAR (100) NULL,
    [OperationId] INT            NOT NULL
);

CREATE TABLE [dbo].[AccountTransaction] (
    [AccountId]   UNIQUEIDENTIFIER NOT NULL,
    [Timestamp]   DATETIME         NOT NULL,
    [OperationId] INT              NOT NULL,
    [Amount]      MONEY            NOT NULL
);

insert dbo.Operation (Description, OperationId) values ('Deposit', 1), ('Withdraw', 2)

Now I can compile the solution.