How do delete conditionally in a many-to-many relation

[cellulosa]

I have a many-to-many relation between users and projects.
I want to be able to allow a user to delete a project if the project is attached to that user.

I can retrieve project data for a given user using the many-to-many reference object (assuming this is the intended way?):

db.query.usersOnProjects.findMany({
	where: ({ userId }, { eq }) => eq(userId, id),
	with: {
		project: true
	}
})

But I am unable to delete a project on condition. With that I mean, if I db.delete(usersOnProjects), then only the row in the relation table is deleted, not the the project.

On the other hand, if I run db.delete(project) I can where() by projectId, but have no way of including a userId condition.

this is my schema:

// user
export const user = pgTable('user', {
	id: text('id').primaryKey()
	username: citext('username').unique().notNull(),
});

export const userRelations = relations(user, ({ many }) => ({
	usersOnProjects: many(usersOnProjects),
}));

// project
export const project = pgTable('project', {
	id: text('id').primaryKey(),
	name: citext('name').notNull().unique(),
});

export const projectRelations = relations(project, ({ many }) => ({
	usersOnProjects: many(usersOnProjects)
}));

// userOnProjects
export const usersOnProjects = pgTable(
	'usersOnProjects',
	{
		userId: text('userId').notNull()
		projectId: text('projectId').notNull()
	},
	({ userId, projectId }) => ({
		pk: primaryKey({ columns: [userId, projectId] })
	})
);

export const usersOnProjectsRelations = relations(usersOnProjects, ({ one }) => ({
	project: one(project, {
		fields: [usersOnProjects.projectId],
		references: [project.id]
	}),
	user: one(user, {
		fields: [usersOnProjects.userId],
		references: [user.id]
	})
}));