GraphQL relay connectionFromArraySlice

Question

There isn't any documentation for how the array meta info (arrayLength and sliceStart) should be implemented using facebook's graphql-relay-js helper library.

https://github.com/graphql/graphql-relay-js/issues/199

I managed to get it to work using the following implemention however I am guessing there is an easier/more correct way to do this.

Retrieve rows and row count from database

function transformRole(role: Role) {
 return { ...role, roleId: role.id };
}
async function getRolesSlice({ roleId, after, first, last, before }: any): Promise<[Role[], number]> { 
 const queryBuilder = repository.createQueryBuilder();
 if (roleId !== undefined) {
 queryBuilder.where('id = :roleId', { roleId });
 }
 if (before) {
 const beforeId = cursorToOffset(before);
 queryBuilder.where('id < :id', { id: beforeId });
 }
 if (after) {
 const afterId = cursorToOffset(after);
 queryBuilder.where({
 id: MoreThan(Number(afterId))
 });
 }
 if (first === undefined && last === undefined) {
 queryBuilder.orderBy('id', 'ASC');
 }
 if (first) {
 queryBuilder.orderBy('id', 'ASC').limit(first);
 }
 if (last) {
 queryBuilder.orderBy('id', 'DESC').limit(last);
 }
 return Promise.all([
 queryBuilder.getMany()
 .then(roles => roles.map(transformRole)),
 repository.count() // Total number of roles
 ]);
}

Roles resolver

resolve: (_, args) =>
 getRolesSlice(args)
 .then(([results, count]) => {
 const firstId = results[0] && results[0].roleId;
 let sliceStart = 0;
 if (args.first) {
 sliceStart = firstId;
 }
 if (args.last) {
 sliceStart = Math.max(firstId - args.last, 0);
 }
 if (args.after && args.last) {
 sliceStart += 1;
 }
 return connectionFromArraySlice(
 results,
 args,
 {
 arrayLength: count + 1,
 sliceStart
 }
 );
 })
 },

Edit:

This is what I came up with which is a little cleaner and seems to be working correctly.

const initialize = () => {
 repository = getConnection().getRepository(Role);
}
function transformRole(role: Role) {
 return { ...role, roleId: role.id };
}
function getRolesSlice(args: any):
 Promise<[
 Role[],
 any,
 { arrayLength: number; sliceStart: number; }
 ]> {
 if (!repository) initialize();
 const { roleId, after, first, last, before } = args;
 const queryBuilder = repository.createQueryBuilder();
 if (roleId !== undefined) {
 queryBuilder.where('id = :roleId', { roleId });
 }
 if (before !== undefined) {
 const beforeId = cursorToOffset(before);
 queryBuilder.where({
 id: LessThan(beforeId)
 });
 }
 if (after !== undefined) {
 const afterId = cursorToOffset(after);
 queryBuilder.where({
 id: MoreThan(Number(afterId))
 });
 }
 if (first !== undefined) {
 queryBuilder.orderBy('id', 'ASC').limit(first);
 } else if (last !== undefined) {
 queryBuilder.orderBy('id', 'DESC').limit(last);
 } else {
 queryBuilder.orderBy('id', 'ASC');
 }
 return Promise.all([
 queryBuilder.getMany()
 .then(roles => roles.map(transformRole))
 .then(roles => last !== undefined ? roles.slice().reverse() : roles),
 repository.count()
 ]).then(([roles, totalCount]) =>
 [
 roles,
 args,
 {
 arrayLength: totalCount + 1,
 sliceStart: roles[0] && roles[0].roleId
 }
 ]
 );
}
// Resolver
roles: {
 type: rolesConnection,
 args: {
 ...connectionArgs,
 roleId: {
 type: GraphQLString
 }
 },
 resolve: (_, args) =>
 getRolesSlice(args)
 .then((slice) => connectionFromArraySlice(...slice))
},