Pass query and function to another function

Question

I have a method which works fine:

 member this.GetItems = 
        let db = dbSchema.GetDataContext()             
        let getQuery = 
            query {
                for row in db.ItemsTable do
                select row
            }
        getQuery 
        |> Seq.map (fun e -> new Item(e.ItemId, e.ItemName ))
        |> Seq.toArray

It make the select query to database, transforms each record to object and returns an array of such objects.

I want to split this method to two. First one must be more general. It gets query and function to transform record to object.

Here is my code:

member private this.ExecuteSelectQuery(query, transform_function) =
    let db = dbSchema.GetDataContext()             
    query 
    |> Seq.map transform_function
    |> Seq.toArray

member this.GetItems = 
    let db = dbSchema.GetDataContext()             

    this.ExecuteSelectQuery 
        query {
            for row in db.ItemsTable do
            select row
        } 
        (fun e -> new Item(e.ItemId, e.ItemName ))

But I get the errors:

In this expression required type 'a * ('b -> 'c) but there is a type QueryBuilder
This construction can be used only in the case of the method For

How can I fix it ?

Updated:

member private this.ExecuteSelectQuery query transform_function =
    let db = dbSchema.GetDataContext()             
    query 
    |> Seq.map transform_function
    |> Seq.toArray

member this.GetItems = 
    let db = dbSchema.GetDataContext()             

    this.ExecuteSelectQuery 
        query {
            for row in db.ItemsTable do
            select row
        } 
        (fun e -> new Item(e.ItemId, e.ItemName ))

Max Malook Max Malook · Accepted Answer · 2015-02-19T13:31:18

The member function ExecuteSelectQuery expects the arguments as a tuple, so you have to use parentheses.

member private this.ExecuteSelectQuery(query, transform_function) =
    query 
    |> Seq.map transform_function
    |> Seq.toArray

member this.GetItems = 
    use db = dbSchema.GetDataContext()             

    this.ExecuteSelectQuery (
        query {
            for row in db.ItemsTable do
            select row
        }, 
        (fun e -> new Item(e.ItemId, e.ItemName )))

Please consider also the use keyword for binding of DataContext instance to correctly implement the disposable pattern. I've done it in my example.

Pass query and function to another function

1 Answers