Is it possible to change the database schema based on user input and use it without rebooting the web server?

As an example:

  1. The user through the form creates a new entity.
  2. After sending the form to the server, the corresponding model is created and migrated.
  3. Changes are available to other users without rebooting the web server.

Thank.

    2 answers 2

    There is a workaround. Based on a pair of definitions and instances tables.

    The first (definitions) is a description of the classes being created, it has two columns (in addition to id) - name: string and structure: text. In the class we serialize attr_list, it will be a hash, the keys will be the names of the attributes, the values ​​will be their type.

    The second table (instances) is actually objects. It contains columns id, definition_id: integer, instance_id: integer and values: text. Similarly, use serialized values ​​to store the object. In it, the values ​​are a hash from the first table according to the selected object type, the keys remain, but the values ​​change to the actual values ​​of the object fields.

    That is, at first we define some “class” on the fly, save it to the first table, and then build the form and form a new object from it, which is saved in the second table. It remains only to provide standard CRUD methods for manipulating these objects, but this is already a matter of technology.

    class CreateTables < ActiveRecord::Migration def change create_table :definitions do |t| t.string :name, null: false t.text :structure end create_table :instances do |t| t.references :definition, null: false t.integer :instance_id, null: false t.text :values end add_index :instances, :definition_id end end class Definition < ActiveRecord::Base serialize :structure, Hash end class Instance < ActiveRecord::Base serialize :values, Hash end
    • I tried this solution, but with large data sets, requests start to run extremely slowly, I want to do something like a setup (let it be long). - Hunter Killer

    You can only store dynamic data:

    • In Postgre use json / jsonb type
    • Dynamic fields in MongoDB