Removing one-one and one-many references - Mongoose

Question

I have an Assignment schema which has references to Groups and Projects.

Assignment == Group [One-One Relationship]
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Answer 1

In the remove middleware, you're defining the actions to take when a document of the model for that schema is removed via Model#remove. So:

• When a group is removed, you want to remove the group reference to that group's _id from all assignment docs.
• When a project is removed, you want to remove the projects array element references to that project's _id from all assignment docs.

Which you can implement as:

GroupSchema.pre('remove', function(next) {
    var group = this;
    group.model('Assignment').update(
        { group: group._id }, 
        { $unset: { group: 1 } }, 
        { multi: true },
        next);
});

ProjectSchema.pre('remove', function (next) {
    var project = this;
    project.model('Assignment').update(
        { projects: project._id }, 
        { $pull: { projects: project._id } }, 
        { multi: true }, 
        next);
});