Manuel Coffin Posts - Answer Overflow

Manuel Coffin

•Created by Manuel Coffin on 3/15/2025 in #help

What's the difference between additionalFields and customSession?

Hi, it's a bit unclear to me the difference between additionalFields and customSession plugin. I am trying to migrate an app using Prisma, and I have a User schema that have many other fields. My understanding is that I should add those fields under user.additionalFields in auth.ts. However, most of those fields are many to many relationships with other tables, so I cannot use the proper type in additionalFields. For example, I have a table Role, and I want to be able to retrieve roles in my session, so should I do this?

user: {
    additionalFields: {
      roles: {
        type: "", // <- What type should I use here?
      },
  }
}

user: {
    additionalFields: {
      roles: {
        type: "", // <- What type should I use here?
      },
  }
}

I also a Preference table, and I want to have the user preferences in the session. Should I also add the preferences in the additionalFields? That way of extending the User schema seems a bit weird to me. Otherwise, I have tried to add the customSession plugin, like this:

customSession(async ({ user, session }) => {
      const dbUser = await prisma.user.findUnique({
        where: {
          id: user.id,
        },
        include: {
          roles: true,
          preferences: true,
          subscription: true,
        },
      });

      return {
        user: {
          ...user,
          roles: dbUser?.roles.map((role) => role.name),
          preferences: {
            distanceUnit: dbUser?.preferences?.distanceUnit,
            elevationUnit: dbUser?.preferences?.elevationUnit,
          },
          subscriptionStatus: dbUser?.subscription?.status,
        },
        session,
      };
    }),

customSession(async ({ user, session }) => {
      const dbUser = await prisma.user.findUnique({
        where: {
          id: user.id,
        },
        include: {
          roles: true,
          preferences: true,
          subscription: true,
        },
      });

      return {
        user: {
          ...user,
          roles: dbUser?.roles.map((role) => role.name),
          preferences: {
            distanceUnit: dbUser?.preferences?.distanceUnit,
            elevationUnit: dbUser?.preferences?.elevationUnit,
          },
          subscriptionStatus: dbUser?.subscription?.status,
        },
        session,
      };
    }),

Which is the way I would like to store those data in my session, the problem here is that the types are not inferred unless I also add additionalFields. I guess my questions would be: How can I simply add custom fields to my session that are also inferred? Could you explain the difference between additionalFields and customSession? Is there a way to have many-to-many relationships in additionalFields?

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