Question: Using dataloader-sequelize with multiple databases

[rcpu]

Hi, I am having an application which is having multiple databases, with same schema structure. When a request arrives based on the user, we resolve it to the right database models dynamically.

Is there any examples on switching the data loader context dynamically.

Code Snippet; Query Schema: attendances: { type: new graphql.GraphQLList(companyDB.StaffAttendance.GQLStaffAttendance), args: defaultListArgs(companyDB.StaffAttendance), resolve: resolver( function (findOptions, args, context, info) { let user = session.get('user');

WOULD LIKE TO UPDATE THE DATALOADER CONTEXT HERE

                    return userDB(user, context).StaffAttendance;
                }, {
                    before: (findOptions, args, context, info) => {
                        findOptions = resolveArgs(findOptions, args);
                        return findOptions;
                    }
                })
        },

Default dataloaderContext

module.exports = expressGraphql({ schema: schema, graphiql: false, context(req) { const dataloaderContext = dataloader.createContext(companyDB.sequelize); resolver.contextToOptions = { dataloaderContext: [EXPECTED_OPTIONS_KEY] }; return { ...req, dataloaderContext }; }, formatError: formatError });

[mickhansen]

So all context to options does is translate some context value to some options value. You could do this yourself via before hooks

[scarlac]

Here's a nasty hack to make it work for multiple databases for those interested:

const context1 = createContext(sequelize1);
const context2 = createContext(sequelize2);

return {
  ...context1,
  loaders: {
    ...context1.loaders,
    ...context2.loaders,
  },
};

However this method is brittle and may break with any upgrade to this library or dataloader-sequelize. Use at your own risk!

[mickhansen]

@scarlac that should work yeah, assuming no shared model names across the two databases. I guess to make it less brittle we could provide an official mergeContexts method for cases like these.

[scarlac]

@mickhansen That would be great. Our situation is that we have 1 schema but several data sources so we'd have no conflicts. Should I make a PR?

[stale[bot]]

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