Norm - Querying entries within generics causes type mismatch compilation error-CodePudding

I write a web application in the nim programming language and use norm as my ORM.

There I follow the standard repository pattern, meaning you have associated with a given URL a controller which calls services that contain business logic on what should happen on the database, which call repositories to perform the actual queries.

I have a generic repository that performs various very repetitive queries for me. The following query for example fetches a list of all entries related to a "Campaign" that has a specific name:

import norm/[model, sqlite]
import <path to the file with the definitions of the used Model and newModel>


proc getCampaignList*[M: Model](connection: DbConn, campaignName: string, modelType: typedesc[M]): seq[M] =
    ##[ Retrieves all rows/entries for a campaign with the given name and 
    returns them as Model M. 
    
    ``campaignName`` must be exactly equal to the name of the targetted campaign,
    the comparison is case-sensitive.]##
    mixin newModel

    var entries: seq[M] = @[]
    entries.add(newModel(M))
    
    connection.select(entries, "campaign_id.name = ?", campaignName)

    result = entries

This works fine if I call the proc directly. I have, however, also been writing generic procs that build controller-procs for me as my application is very CRUD heavy and thus very repetitive. So I have a genericService and more.

When used within these several layers of generics, the proc breaks mysteriously:

type mismatch: got <DbConn, seq[DiaryEntryRead], string, DbValue>
but expected one of:
...
<Unnecessary examples>
...
proc select[T: Model](dbConn; objs: var seq[T]; cond: string;
                      params: varargs[DbValue, dbValue])
  first type mismatch at position: 4
  required type for params: varargs[DbValue]
  but expression 'dbValue(campaignName)' is of type: DbValue

expression: select(connection, entries, "campaign_id.name = ?", dbValue(campaignName))

I'm not sure why this suddenly happens when it worked perfectly fine before. What could my issue be?

CodePudding user response：

The issue appears to be somewhere in the interaction between nim generics and converting types properly into varargs (Thanks to "Solitude" and "Rika" from nim's discord server for the help!). I haven't dug any deeper into it as to why this happens, but at very least it's fixable.

The parameters you throw in as the parameters at position 4 and onwards can just be converted into DbValue and stuffed into an array or seq. Below the way I solved this and "foolproofed" the proc (I used an array because why use a seq when the number of parameters is static and you know it ahead of time):

proc getCampaignList*[M: Model](connection: MyDbConn, campaignName: string, modelType: typedesc[M]): seq[M] =
    ##[ Retrieves all rows/entries of a campaign with the given name and 
    returns them as Model M. 
    
    ``campaignName`` must be exactly equal to the name of the targetted campaign,
    the comparison is case-sensitive.]##
    mixin newModel

    var entries: seq[M] = @[]
    entries.add(newModel(M))
    
    let queryParams: array[1, DbValue] = [campaignName.dbValue()]
    connection.select(entries, "campaign_id.name = ?", queryParams)

    result = entries