What is it

Arguments in Graphql resolvers provide a way for other node/entity connections and sub-fields to retain context from the parent node/entity.

const resolvers = {
  Query: {
    user(parent, args, contextValue, info) {
      return users.find((user) => user.id === args.id);
    },
  },
};

parent

The return value of the resolver for this field's parent (previous resolver in the resolver chain).

At top-level fields without a parent, this value is obtained from the rootValue function passed to Apollo server's constructor.

args

An object that contains all GraphQL arguments provided for this field.

# query
query {
  user(id: "4")
}

# arg obj passed to user resolver
args = {
  "id": "4"
}

# resolver
const resolvers = {
  Query: {
    user(parent, args, contextValue, info) {
      return users.find((user) => user.id === args.id);
      # args.id = "4"
    },
  },
};

contextValue

Object shared across all resolvers executing for a particular operation.

Use this to share per-operation state.

• use this for auth information, dataloader instances, database connections, and anything else to track across resolvers.

When calling a service method on a resolver field, to keep the context, you might have to pass the context explicitly as another parameter.

Caveat

You cannot use context to reference a value from another resolver as a general purpose cache.

When you store a value from another resolver into context and make a call via context.value from another resolver, there is no guarantee that the context.value will not be null.

• Long-running resolver function may not complete in time for another field to reference. Ideally every resolver should be separate from each other to avoid sharing state between each other and tightly coupling.

info

Information about the operation's execution state.

• field name, path to the field from the root, and etc.