Feature: Add support for custom GraphQL scalars `@gql(scalars: { website: "AWSURL" })`

[Bell]

Right now it seems like only fields that are named url or email have been hardcoded to use the AWSURL and AWSEmail scalar types from AWS, however I would like to be able to use these types on fields like urlPhoto or something like secondaryEmail.

As seen here:

prisma-appsync/packages/generator/src/compiler.ts

Lines 859 to 868 in 37b4a68

 if (type === 'String') { 
     switch (field.name.toLocaleLowerCase()) { 
         case 'email': 
             type = 'AWSEmail' 
             break 
         case 'url': 
             type = 'AWSURL' 
             break 
     } 
 } 

Would it be possible to use triple slash comments in the Prisma schema to define which fields turn up as what scalar types in the GraphQL schema?

[Sylvain]

Possibly yes, but would need to find the right syntax...

There is already a custom notation in place (not documented yet) that allows customising the generated GraphQL schema.

/// @gql(queries: { list: null, count: "countyPosts" }, fields: { text: null }, subscriptions: null)
model Post {
    text  String?
    urlPhoto  String?
}

The above notation equals to:

• Remove listPosts
• Rename countPosts to countyPosts
• Remove text field
• Remove all subscriptions

One option could be:

/// @gql(scalars: { urlPhoto: "AWSURL" })
model Post {
    urlPhoto  String?
}

Implementing the above would be quite simple, as the code to read the @gql directive is already in place.

What do you think?

[Bell]

I think that makes sense yes! Until documentation gets written, is there a way to know where exactly the code involving that custom notation is in place?

[Sylvain]

Parsing the @gql directive as a JSON object is done here:

prisma-appsync/packages/generator/src/compiler.ts

Lines 367 to 375 in 37b4a68

 const gqlDirectives = directives.match(gqlRegex) 
  
 if (gqlDirectives) { 
     for (let i = 0; i < gqlDirectives.length; i++) { 
         const str = replaceAll(gqlDirectives[i].replace(gqlRegex, '$1'), find, replace) 
         // eslint-disable-next-line no-new-func 
         gql = merge({}, gql, new Function(`return ({${str}})`)()) 
     } 
 } 

The following is the config object where to add _scalars: gqlObject?.scalars || {}:

prisma-appsync/packages/generator/src/compiler.ts

Lines 393 to 406 in 37b4a68

 const gqlOutput: { 
     _model: boolean 
     _fields: any 
     _usesQueries: boolean 
     _usesMutations: boolean 
     _usesSubscriptions: boolean 
     [key: string]: any 
 } = { 
     _model: gqlObject?.model !== null, 
     _fields: gqlObject?.fields || {}, 
     _usesQueries: false, 
     _usesMutations: false, 
     _usesSubscriptions: false, 
 } 

Here is where the check to ignore fields is done:

prisma-appsync/packages/generator/src/compiler.ts

Lines 544 to 567 in 37b4a68

     const isFieldIgnored = gqlConfig?._fields?.[field.name] === null 
  
     if (!field.isGenerated && !isFieldIgnored) { 
         fields.push({ 
             name: field.name, 
             type: field.type, 
             scalar: this.getFieldScalar(field), 
             isRequired: this.isFieldRequired(field), 
             isList: this.isFieldList(field), 
             isEnum: this.isFieldEnum(field), 
             isEditable: !this.isFieldGeneratedRelation(field, model), 
             isUnique: this.isFieldUnique(field), 
             ...(field.relationName && { 
                 relation: { 
                     name: this.getFieldRelationName(field, model), 
                     kind: this.getFieldRelationKind(field), 
                     type: this.getFieldScalar(field), 
                 }, 
             }), 
             directives, 
             sample: this.getFieldSample(field), 
         }) 
     } 
 }) 

For example, we could do:

const scalar = gqlConfig?._scalars?.[field.name] || this.getFieldScalar(field)

[Sylvain]

@Tenrys do you want to work on a PR for this feature?

[Sylvain]

Will be released as part of 1.0.0-rc.6 (you can also try it now with prisma-appsync@1.0.0-preview.6.6).