F# Type Providers and Continuous Integration

Question

The type definition of an F# type provider often requires a constant expression, e.g. for the SQL type provider:

type dbSchema = SqlDataConnection<"Data Source=MySqlServer;Initial Catalog=MyDatabase;">

However, when committing the code to SCM, and further having a build server doing its thing, you probably don’t want to use the same connection string, but rather the connection string of a SQL server database that is generated from the build process.

Is there a solution for this problem?

It would be really nice to be able to make this work, as it would provide a compile-time check of the database access code.

Update The solution proposed by @tomaspetricek worked very well, but I had to add a provider name to the connection string:

<add name="DbConnectionString" providerName="System.Data.SqlClient" connectionString="Data Source=MySqlServer;Initial Catalog=MyDatabase;"/>

It would be even better if that string was sourced from a configuration file. — Robert Harvey, Sep 23 '13 at 21:32
@RobertHarvey Indeed, that's exactly what can easily be done ;-) — Tomas Petricek, Sep 23 '13 at 21:59

score 15 · Accepted Answer · answered Sep 23 '13 at 21:54

You can certainly specify the connection string using a key in a configuration file (see MSDN documentation):

SqlDataConnection<ConnectionStringName="...", ConfigFile="app.config">

In general, a type provider may require some constant expression, but I think most of the widely used ones provide a way for avoiding this. For example, SqlDataConnection can read the setting from configuration file, other standard F# type providers allow specifying LocalSchemaFile that allows you to specify the necessary structure locally (e.g. *.dbml file for SQL).

The F# Data type providers can take URL to a remote file, but they can also take local file. So I think that there should always be a way to specify the information without specifying a constant connection string (etc.) - but feel free to ask about specific providers.

The links links "Please see Walkthrough: Accessing a SQL Database by Using Type Providers" are definitely broken on [this page](https://fsprojects.github.io/FSharp.Data.TypeProviders/sqldata.html) — Pavel Voronin, Mar 18 '20 at 11:32
Nowadays it should support appSettings and env variables as well. ;-) Actually, I'd prefer to have some standard "protocol" which I need to implement in a separate assembly and then reference this assembly in TypeProvider. — Pavel Voronin, Mar 18 '20 at 11:52

F# Type Providers and Continuous Integration

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