I'm trying to have a powerful client-side querying API, where the client can specify which table to run the query in and the conditions to the query. Of course that's no replacement to full-blown LINQ or SQL, it's just so the JS client can make complex queries on tables, without joins.
Now, most of it is done, as below. The client sends me a JSON-serialized Predicate
(which I deserialize with JSON.NET), and I can easily compose it into a query.
module Query =
open System.Linq
open FSharp.Data.Sql.Common
open FSharpComposableQuery
type Predicate =
| All
| Greater of string * System.IComparable
| GreaterEq of string * System.IComparable
| Lesser of string * System.IComparable
| LesserEq of string * System.IComparable
| Equal of string * obj
| Diff of string * obj
| And of Predicate * Predicate
| Or of Predicate * Predicate
| Not of Predicate
let satisfies (table : IQueryable<SqlEntity>) =
<@ fun p -> query {
for c in table do
if p c
then yield c
} @>
let rec eval t =
match t with
| All -> <@ fun _ -> true @>
| Greater (column, n) -> <@ fun (c : SqlEntity) -> c.GetColumn column > n @>
| GreaterEq (column, n) -> <@ fun c -> c.GetColumn column >= n @>
| Lesser (column, n) -> <@ fun c -> c.GetColumn column < n @>
| LesserEq (column, n) -> <@ fun c -> c.GetColumn column <= n @>
| Equal (column, n) -> <@ fun c -> c.GetColumn column = n @>
| Diff (column, n) -> <@ fun c -> c.GetColumn column <> n @>
| And (p1, p2) -> <@ fun c -> (%eval p1) c && (%eval p2) c @>
| Or (p1, p2) -> <@ fun c -> (%eval p1) c || (%eval p2) c @>
| Not p -> <@ fun c -> not((%eval p) c) @>
let predicate = Or (Equal ("myColumn", "myValue"), Equal ("myColumn", "myOtherValue"))
let t = query {
for c in <someDataProvidedTable> do
select (c :> SqlEntity)
}
let result = query { yield! (%satisfies t) (%eval predicate) } |> Seq.toArray
module DataLayer =
open FSharp.Data.Sql
open FSharp.Data.Sql.Common
let [<Literal>] ConnectionString = "Data Source=" + __SOURCE_DIRECTORY__ + @"/db.sqlite3;Version=3"
type Sql = SqlDataProvider<
ConnectionString = ConnectionString,
DatabaseVendor = Common.DatabaseProviderTypes.SQLITE,
IndividualsAmount = 1000,
UseOptionTypes = true >
let ctx = Sql.GetDataContext()
let db = ctx.Maint
All that is left to parameterize is... the table. DataLayer.db
has table objects equivalent to my tables, and my functions accept these table objects. But I want the client to be able to send me the table as a string, and I inspect DataLayer.db
to retrieve a table from it.
Now, I know I could solve this by having a dictionary from string to table object. But that would make the whole construct less usable (we're generating the schema and the client from an external DSL). Of course, I have tried DataLayer.db.GetType().InvokeMethod
, but I get the following exception no matter what the parameters are.
System.MissingMethodException: Method 'FSharp.Data.Sql.Runtime.SqlDataContext.FsmIssue' not found.
at System.RuntimeType.InvokeMember (System.String name, System.Reflection.BindingFlags bindingFlags, System.Reflection.Binder binder, System.Object target, System.Object[] providedArgs, System.Reflection.ParameterModifier[] modifiers, System.Globalization.CultureInfo culture, System.String[] namedParams) [0x008a0] in <dca3b561b8ad4f9fb10141d81b39ff45>:0
at System.Type.InvokeMember (System.String name, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object target, System.Object[] args) [0x00000] in <dca3b561b8ad4f9fb10141d81b39ff45>:0
at <StartupCode$FSI_0062>.$FSI_0062.main@ () [0x0001a] in <906a7cff96cb466bbad0babb35abf8de>:0
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00038] in <dca3b561b8ad4f9fb10141d81b39ff45>:0
Stopped due to error
So, is anyone able to help me?
You may use define function like getTable below, which will return IQueryable for given context and table fullname:
note that tableFullName is DB specific, if you look at: FSharp.Data.Sql.Schema.Table source code you notice it's based on Schema and TableName where record members are set in specific providers:
EDIT: simpler way to toubleshot/find actual full table name
In case of doubts/problems with table full name you can rely on
DB.dataContext
which utilizes full name for variety of database objects.UPDATE: question in comments regarding accessing Create
similarly to accessing all records, create can be accessed via reflection as:
this particular example utilizes (string * obj) seq as parameter, as seen in FSharp.Data.Sql.SqlDesignTime in create3. It can be adjusted to manner used in create1 or create2, or any other required.