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]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.