SqlDataProvider - Compose a where clause dynamically and execute the command - linq

Question

I have the following requirement:
Query a SQL table with a dynamically generated where clause that should be composed from a list at run time.
[<Literal>]
let connectionString = "Data Source=..."
type sql = SqlDataProvider<
ConnectionString = connectionString,
DatabaseVendor = Common.DatabaseProviderTypes.MSSQLSERVER,
UseOptionTypes = true>
let ctx = sql.GetDataContext()
type Key = {k:string;v:string}
let findCustomersByKeys (keys:Key list) =
query{
for c in ctx.Dbo.Customers do
where (keys.Any(fun k -> c.k = k.k && c.v = k.v))//this is what i wish i could do
select c
}
Is there a way to do it in F# with SqlDataProvider?
Any other technique?

Answer 1

You can use quotations to construct the predicate dynamically, and splice that directly into the query expressions since query expressions are actually compiled into quotations themselves.
The predicate is built by folding over the keys, recursively splicing or-conditions onto an initial condition of false. But because we can't close over c here, we also need to wrap each condition in a function and thread the argument through the predicate chain.
open Microsoft.FSharp.Quotations
type Key = {k:string;v:string}
let findCustomersByKeys (keys:Key list) =
let predicate =
keys
|> List.fold
(fun (acc: Expr<Key -> bool>) k ->
<# fun c -> (%acc) c || c.k = k.k && c.v = k.v #>)
<# fun c -> false #>
query {
for c in ctx.Dbo.Customers do
where ((%predicate) c)
select c
}