将查询和函数传递给另一个函数

Question

我有一个很好的方法：

 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

它对数据库进行选择查询，将每条记录转换为对象并返回一个此类对象的数组。

我想将此方法一分为二。第一个必须更一般。它获取查询和函数将记录转换为对象。

这是我的代码：

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 ))

但我得到了错误：

• 在这个表达式中需要类型 'a * ('b -> 'c) 但有一个类型 QueryBuilder
• 这种结构只能用于 For 方法的情况

我该如何解决？

更新：

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 ))

Answer 1

成员函数ExecuteSelectQuery 期望参数为元组，因此您必须使用括号。

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 )))

还请考虑use 关键字用于绑定DataContext 实例以正确实现一次性模式。我已经在我的例子中做到了。