How to change DB connections on the fly with GraphQL? - database

Question

We have a GraphQL server setup which uses the exact same set of GraphQL calls on different client systems. These clients have the same exact tables/structures which do not change.
I'd like to make a GraphQL calls which indicate which DB connection to use. OR if there is a similar alternative with GraphQL, I'm all ears.
I've been Googling, forum diving, and document scanning for a while...

Answer 1

One possible solution is to create a directives.
const typeDefs = gql`
directive #db(client: DbClient) on FIELD_DEFINITION
type DbClient {
DB_CLIENT_1
DB_CLIENT_2
}
type Query {
users: [User] #db
}
`;
// Directive
// db client connection config
const dbConnectionConfig = {
DEFAULT : {...},
DB_CLIENT_1: {...},
DB_CLIENT_2: {...}
}
class DbClientDirective extends SchemaDirectiveVisitor {
public visitFieldDefinition(field) {
const { resolve = defaultFieldResolver } = field;
const { client } = this.args;
field.args.push({
name: 'client',
type: GraphQLString
});
field.resolve = async function (
source,
{ client, ...otherArgs },
context,
info,
) {
let connectionConfig = dbConnectionConfig.DEFAULT;
if(Object.prototype.hasOwnProperty.call(dbConnectionConfig, client)) {
connectionConfig = dbConnectionConfig[client];
}
/**
create a DB client with the given config. Even you can persist the DB connection is a hashMap such that you don't need to establish a new connection every time.
**/
const dbSession = new DbClient(connectionConfig);
// put the dbSession in a context such that it can be used by the resolver.
context.dbSession = dbSession;
return resolve.call(this, source, otherArgs, context, info);
};
field.type = GraphQLString;
}
}
// UserResolver.js
const UserResolver = {
Query: {
users(async (parent, args, context, info) => {
const dbSession = context.dbSession;
// use the dbSession to fetch the results. Note, here resolve need not to know about the db client details.
return dbSession.findAll();
}
}
const resolvers = merge(
UserResolver
);
const server = new ApolloServer({
typeDefs,
resolvers,
schemaDirectives: {
date: DbClientDirective
}
});
server.listen().then(({ url }) => {
console.log(`🚀 Server ready at ${url}`);
});
You can now pass client argument to a user query to indicate which DB connection to use.
Example 1 - this will use DEFAULT as DB client
query {
users {
name
userId
}
}
Example 2 - this will use DB_CLIENT_1 as DB client
query {
users(client: DB_CLIENT_1) {
name
userId
}
}