What is this code add_to_serializer in all these plugins

I have seen this code in discourse_signatures plugin

User.register_custom_field_type('see_signatures', :boolean)
User.register_custom_field_type('signature_url', :text)
User.register_custom_field_type('signature_raw', :text)

if SiteSetting.signatures_enabled then
  add_to_serializer(:post, :user_signature, false) {
    if SiteSetting.signatures_advanced_mode then
      object.user.custom_fields['signature_raw']
    else
      object.user.custom_fields['signature_url']
    end
  }

  # I guess this should be the default @ discourse. PR maybe?
  add_to_serializer(:user, :custom_fields, false) {
    if object.custom_fields == nil then
      {}
    else
      object.custom_fields
    end
  }
end

In discourse national flags plugin

User.register_custom_field_type('nationalflag_iso', :text)

if SiteSetting.nationalflag_enabled then
  byebug;
  add_to_serializer(:post, :user_signature, false) {
    object.user.custom_fields['nationalflag_iso']
  }
  byebug;
  # I guess this should be the default @ discourse. PR maybe?
  add_to_serializer(:user, :custom_fields, false) {
    if object.custom_fields == nil then
      {}
    else
      object.custom_fields
    end
  }
end

I am not able to understand what is add_to_serializer is doing.

I checked in def add_to_serializer

def add_to_serializer(serializer, attr, define_include_method=true, &block)
  klass = "#{serializer.to_s.classify}Serializer".constantize rescue "#{serializer.to_s}Serializer".constantize

  klass.attributes(attr) unless attr.to_s.start_with?("include_")

  klass.send(:define_method, attr, &block)

  return unless define_include_method

  # Don't include serialized methods if the plugin is disabled
  plugin = self
  klass.send(:define_method, "include_#{attr}?") { plugin.enabled? }
end

I understand that User.register_custom_field_type('signature_raw', :text) will register a custom field type to User object. But what is add_to_serializer doing? I am not able to understand, can you explain me in plain english?

It’s essentially adding to the information that Discourse serializes out when sending that model to the client. For example, you may see a request to this endpoint when loading up a topic page:

http://meta.discourse.org/t/2349082394.json

which returns some payload like this:

{
  title: "Some topic title",
  archetype: 'regular',
  category_id: 7,
  post_stream: { posts: [...] },
  posts_count: 15,
  (etc etc.. lots more info about the topic in question)
}

Which is the json representation of a Discourse topic.

If I want to know more about the topic because of additional ‘stuff’ I do in my plugin, I can put in a line like

add_to_serializer :topic, :flag_name do
  object.flag_name # <- NB that 'object' here is the topic being serialized
end

(Also, by default, this method simply sends the specified message to ‘object’, meaning that

add_to_serializer :topic, :flag_name

is the same as

add_to_serializer :topic, :flag_name do
  object.flag_name
end

)

Once I’ve added the method to the serializer, I can end up with JSON output which includes that additional info

{
  title: "Some topic title",
  archetype: 'regular',
  category_id: 7,
  post_stream: { posts: [...] },
  posts_count: 15,
  flag_name: "some flag name"
  ...
}

Also note that you could achieve the same thing by overwriting the TopicSerializer class (which is exactly what the code snippet you’ve provided is doing)

# plugin.rb
TopicSerializer.class_eval do
  attributes :flag_name
  def flag_name
    object.flag_name
  end
end
16 Likes

Hi,
When running the following code,

TopicSerializer.class_eval do
  attributes :flag_name
  def flag_name
    object.flag_name
  end
end

I was getting the error “block in activate!’: uninitialized constant TopicSerializer (NameError)”. I think I have to “import” or “require” the TopicSerializer dependency. Can you please tell me what would be the dependency, as I am not able to figure it out.

1 Like

Add this directly above your code require_dependency 'topic_serializer'

require_dependency 'topic_serializer'
class ::TopicSerializer
  attributes :flag_name
  def flag_name
    object.flag_name
  end
end
1 Like

Hi thanks, but I got the error " `load’: No such file to load – topic_serializer (LoadError)". Does it pull from the app/serializers folder? I checked in that folder, I could find topic_list_serializer.rb, and many other related to topic, but couldnt find topic_serializer.rb

1 Like

Right! Try TopicViewSerializer.

require_dependency 'topic_view_serializer'
class ::TopicViewSerializer
  attributes :flag_name
  def flag_name
    object.flag_name
  end
end
4 Likes

Heyy, I have added a custom field to my category edit box.

When I submit the form, I can see something these fields are submitted in the js console
custom_fields[default_tag][]:good-feedback custom_fields[default_tag][]:one-more-tag

in my main plugin file, I am doing

add_to_serializer(:basic_category, :default_tag){object.custom_fields[“default_tag”]}

My custom fields aren’t getting saved to the db.

does doing:

add_to_serializer(:basic_category, :default_tag, false ){object.custom_fields[“default_tag”]}

now work?

I had solved it that time by adding a function on :before_action event and converted the array to a delimited string and vice versa while retrieving.

I didn’t actually dig into why an array couldn’t be stored as custom field out of the box.

1 Like

So this might streamline the code potentially?

Yes it would if it worked in this case. I’ll try this in sometime and get back to you.

1 Like

Poor you that must’ve been painful at the time :wink:

1 Like

It was a sunday evening and curiosity took over. It was somewhat painful but fun.
It was something that @pfaffman was trying to do.

No pain no gain :wink:

1 Like

haha, so true! …

1 Like

Hello, I have the same issue (custom_fields are submitted in the js console, but are not getting saved to the db) I used the add_to_serializer(:basic_category, :default_tag, false ){object.custom_fields[“default_tag”]} way in my main plugin file.

Would you still reccomend this solution?

1 Like

There are a lot of questions arising here. Custom fields of what first of all?

I’m working on a plugin to automate discourse group syncing with ldap. I added a custom field to Group (ldap_dn) to save the ldap group name in. I’m trying to retrieve the custom_field value from an input field that i added in the membership plugin-outlet and save that to the db to later use it.

To do so i added this to my plugin.rb file

Group.register_custom_field_type(‘ldap_dn’, :text)
Group.preload_custom_fields<< “ldap_dn” if
Group.respond_to? :preloaded_custom_fields

if SiteSetting.groups_sync_enabled then
add_to_serializer(:group_show, :custom_fields, false) {
object.custom_fields
}
end

I’m new to rails and ember so I’m not sure if there is another step I should be doing in order to get the custom_fields saved to the db, or where the problem lies.

I think if you add
register_editable_group_custom_field 'field_name'
to your plugin.rb

that should do the job

Note:
Serializer is used to send the data to the client and not receive it.

1 Like

ahh okay! I’m a newbie so this might be a very ‘duh’ question, but to receive the data, do I do so using the api?

1 Like

My solution will give a green flag to your field when it comes through to the server. So its about receiving the data

1 Like