Filter/Where as a standalone concept

[bajtos]

Refactor the current implementation of LoopBack's Filter to allow other packages to leverage the filtering implementation and/or support LoopBack's Filter syntax.

1. The syntax of Filter/Where objects should be well defined and properly documented, to allow 3rd-party implementations to understand all possible values.

2. There should be TypeScript typings describing Filter, Where, etc., these typings must be accessible independently on @loopback/repository (e.g. via a new package).

3. The implementation used by our memory connector should be refactored/extracted into a package that can be used independently from juggler (something like https://www.npmjs.com/package/loopback-filters). It's important to update the connector to use that new package, to ensure there is only single reference implementation.

Nice to have:

• JSON Schema describing Filter syntax
• Some sort of a test suite to allow 3rd-party implementations to verify conformance

[rem-code-s]

Really looking forward to this! The only way around the filter and where missing types is by declaring them in the 3rd-party application i suppose?

[achrinza]

@RAW4RMCS Currently, these can be imported from @loopback/repository. However, that package bundles other things such as the Juggler ORM, repository classes, etc.

See: https://loopback.io/doc/en/lb4/apidocs.repository.filter.html

[rem-code-s]

@achrinza hmm maybe this isn't the fix for the issue i'm currenly facing if i understand your response correctly,
The issue i'm facing is the following;

I'm using Nswag for generating a frontend client to consume the api endpoints based on the openapi spec,

Example of the generated code base on a controller + model;

/**
     * @param filter (optional) 
     * @return Container model instance
     */
    getContainerById(id: number, filter: any | undefined): Promise<ContainerWithRelations> {
        let url_ = this.baseUrl + "/containers/{id}?";
        if (id === undefined || id === null)
            throw new Error("The parameter 'id' must be defined.");
        url_ = url_.replace("{id}", encodeURIComponent("" + id));
        if (filter === null)
            throw new Error("The parameter 'filter' cannot be null.");
        else if (filter !== undefined)
            url_ += "filter=" + encodeURIComponent("" + filter) + "&";
        url_ = url_.replace(/[?&]$/, "");

        let options_ = <RequestInit>{
            method: "GET",
            headers: {
                "Accept": "application/json"
            }
        };

        return this.transformOptions(options_).then(transformedOptions_ => {
            return this.http.fetch(url_, transformedOptions_);
        }).then((_response: Response) => {
            return this.processGetContainerById(_response);
        });
    }

    protected processGetContainerById(response: Response): Promise<ContainerWithRelations> {
        const status = response.status;
        let _headers: any = {}; if (response.headers && response.headers.forEach) { response.headers.forEach((v: any, k: any) => _headers[k] = v); };
        if (status === 200) {
            return response.text().then((_responseText) => {
            let result200: any = null;
            let resultData200 = _responseText === "" ? null : JSON.parse(_responseText, this.jsonParseReviver);
            result200 = ContainerWithRelations.fromJS(resultData200);
            return result200;
            });
        } else if (status !== 200 && status !== 204) {
            return response.text().then((_responseText) => {
            return throwException("An unexpected server error occurred.", status, _responseText, _headers);
            });
        }
        return Promise.resolve<ContainerWithRelations>(<any>null);
    }

As shown here in the function the filter has a any type (and it's required), but when i check the swaggerUI the required properties are included in the call. I thought this would fix this issue but i guess it does not.

Do you recommend a client generator for Loopback where this issue doesn't occur?
Sorry if this comment isn't related to this issue.

[achrinza]

@RAW4RMCS Based on the code, the filter is considered optional, hence the any | undefined type.

The filter shown on the Swagger UI is auto-generated by Swagger UI itself.

Also, it seems to be a limitation of nswag to use an any type for the filter, not fully utilizing the OpenAPI 3.0 spec.

A popular OAS3 generator would be https://github.com/OpenAPITools/openapi-generator. However, I've not tried any of the generators myself.