Answers.Body: <p>You would just loop the entry models to collect the IDs (looks ugly, but it's a simple and efficient for loop). But in case you do not need anything else from the models, I'd actually expect your previous approach using the <code>ids</code> method to have better performance.</p>
  
  <pre><code>{% set ids = [] %}
  {% for entry in entry.myEagerLoadedEntries %}
      {% set ids = ids|merge([entry.id]) %}
  {% endfor %}
  </code></pre>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-04-19T21:52:00.187Z
Answers.LastActivityDate: 2016-04-19T21:52:00.187Z
Answers.UserDisplayName: carlcs
Answers.Body: <p>You could use the <a href="https://craftcms.com/docs/templating/craft.entries#indexBy" rel="nofollow">indexBy</a> parameter and the <a href="http://twig.sensiolabs.org/doc/filters/keys.html" rel="nofollow">keys</a> filter:</p>
  
  <pre><code>{# Using indexBy updates the results array to be indexed by the Element ID
     instead of a consecutively numbered array #}
  {% set entries = craft.entries.section('news').with(['featuredImage']).indexBy('id') %}
  
  {# The keys filter returns an array of all the keys within an array,
     discarding the values #}
  {% set entryIds = entries|keys %}
  </code></pre>
  
  <p>This would give you an array of the Element IDs that were retrieved.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-04-20T07:32:20.150Z
Answers.Text: The `indexBy` looks handy (never noticed it in the docs), but in this case it won't work, as the OP needs the IDs of the eager loaded elements.
Answers.UserDisplayName: carlcs
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-04-20T23:15:11.970Z
Answers.Text: Can you elaborate on how this doesn't provide the ids in the format necessary in the question? `indexBy` just updates the ids of the result array to be the Element IDs that are needed, and passing the results through the `keys` filter creates an array of the ids, just like the loop and merge approach. The eager loaded elements are still available via the `entries` variable, and an array of ids is available for use via the `entryIds` variable.
Answers.UserDisplayName: Ben Parizek
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-04-20T23:35:48.083Z
Answers.Text: Hmm.. but thinking about it, it might actually be possible to use that `indexBy` param within the `with` param. That might work. But I'm still thinking eager loading isn't worth it at all in this case. An extra query using the `ids` method is probably performing better as you don't have the (unnecessary) overhead of populating all the models.
Answers.UserDisplayName: carlcs
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-04-21T15:05:15.560Z
Answers.Text: That does sound possible: `with(['featuredImage', { indexBy: 'id' }])` however, I think your right in that it really depends which `ids` are needed and where on the page. Eager loading is about optimizing the querying of relations, and this question is just about getting an array of IDs.  In the case the OP needs both the results and the IDs, I think something like this answer works fine, getting the optimized eager-loaded data, and using `keys` to distill the IDs.  In the case they just need the IDs, there is no real need to add eager-loading to the mix.
Answers.UserDisplayName: Ben Parizek
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-04-20T02:19:04.250Z
Answers.LastActivityDate: 2016-04-20T02:19:04.250Z
Answers.UserDisplayName: Ben Parizek
Body: <p>I have been using the ids() method on the ElementCriteriaModel returned by a call to an entries field within a Twig template to return an array of ids for further processing. </p>
  
  <p>Now I wish to eager-load these entries, but the entries are returned as an array with no access to the ids() method.</p>
  
  <p>Is there an efficient way to get this array of ids within Twig, or would I be better moving this to a plugin?</p>
  
Tags: <templating><eager-loading>
Title: Getting an array of ids from an array of eager-loaded elements within Twig
ThreadText: # Getting an array of ids from an array of eager-loaded elements within Twig
  
  (Asked by: username_0 on 2016-04-19)
  
  I have been using the ids() method on the ElementCriteriaModel returned by a call to an entries field within a Twig template to return an array of ids for further processing.
  
  Now I wish to eager-load these entries, but the entries are returned as an array with no access to the ids() method.
  
  Is there an efficient way to get this array of ids within Twig, or would I be better moving this to a plugin?
  
  **Tags:** templating, eager-loading
  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_1 on 2016-04-19. Score: 3 | Accepted answer
  
  You would just loop the entry models to collect the IDs (looks ugly, but it's a simple and efficient for loop). But in case you do not need anything else from the models, I'd actually expect your previous approach using the `ids` method to have better performance.
  
  ```
  {% set ids = [] %}
  {% for entry in entry.myEagerLoadedEntries %}
      {% set ids = ids|merge([entry.id]) %}
  {% endfor %}
  
  ```
  
  
  ---
  
  ### Answer by username_2 on 2016-04-20. Score: 2
  
  You could use the [indexBy](https://craftcms.com/docs/templating/craft.entries#indexBy) parameter and the [keys](http://twig.sensiolabs.org/doc/filters/keys.html) filter:
  
  ```
  {# Using indexBy updates the results array to be indexed by the Element ID
     instead of a consecutively numbered array #}
  {% set entries = craft.entries.section('news').with(['featuredImage']).indexBy('id') %}
  
  {# The keys filter returns an array of all the keys within an array,
     discarding the values #}
  {% set entryIds = entries|keys %}
  
  ```
  
  This would give you an array of the Element IDs that were retrieved.
  
  > **Comments:**
  > **username_1**: The `indexBy` looks handy (never noticed it in the docs), but in this case it won't work, as the OP needs the IDs of the eager loaded elements.  
  > **username_2**: Can you elaborate on how this doesn't provide the ids in the format necessary in the question? `indexBy` just updates the ids of the result array to be the Element IDs that are needed, and passing the results through the `keys` filter creates an array of the ids, just like the loop and merge approach. The eager loaded elements are still available via the `entries` variable, and an array of ids is available for use via the `entryIds` variable.  
  > **username_1**: Hmm.. but thinking about it, it might actually be possible to use that `indexBy` param within the `with` param. That might work. But I'm still thinking eager loading isn't worth it at all in this case. An extra query using the `ids` method is probably performing better as you don't have the (unnecessary) overhead of populating all the models.  
  > **username_2**: That does sound possible: `with(['featuredImage', { indexBy: 'id' }])` however, I think your right in that it really depends which `ids` are needed and where on the page. Eager loading is about optimizing the querying of relations, and this question is just about getting an array of IDs.  In the case the OP needs both the results and the IDs, I think something like this answer works fine, getting the optimized eager-loaded data, and using `keys` to distill the IDs.  In the case they just need the IDs, there is no real need to add eager-loading to the mix.  
  
  ---
  
  