Working with WP

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# Working with WP_Query

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## Basics
]
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.left-column[
### What is `WP_Query` used for?
]
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**Short version:** Handles all of the logic for retrieving post.red[*] objects from the database.

**Long version:** You're about to find out 😁
]

.footnote[.red[*] Post-_type_ objects, not only posts.]
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.left-column[
### What is `WP_Query` used for?
### How is it used?
]
.right-column[
```php
if ( have_posts() ):
	while ( have_posts() ) : the_post();
		// Your template code
	endwhile;
endif;
```
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## Custom Queries
]
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### Common Uses
]
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* Showing posts in a sidebar or footer
* Showing related posts
* Showing CPT data
]
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### Common Uses
### Creating a Custom Query
]
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* Determine what arguments you need
* Create a new `WP_Query` object
```php
$my_query = new WP_Query( array(
		'post_type'      => 'some_cpt',
		'posts_per_page' => 5,
) );
```
* Run your loop
```php
while ( $my_query->have_posts() ) : $my_query->the_post();
		// Template code here
endwhile;
*wp_reset_postdata();
```
* **Reset WordPress globals with `wp_reset_postdata()`**
]

???
* Why is `wp_reset_postdata()` needed?
* When is `wp_reset_postdata()` needed?
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### Common Uses
### Creating a Custom Query
### Common Parameters
]
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* `posts_per_page` - Number of posts to show at once
* `cat` - Limit posts to a particular category
* `post_type` - Limit posts to one or more post types
* `order` - How to order posts (ascending or descending)
* `orderby` - What data to use to order the posts
]
.footnote[See [all of the options](https://codex.wordpress.org/Class_Reference/WP_Query#Pagination_Parameters) in the Codex.]
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### Common Uses
### Creating a Custom Query
### Common Parameters
### Parameters to avoid
]
.right-column[
* `orderby` = `rand`
* `posts_per_page` = `-1`
* `showposts` (deprecated)
* `post__not_in`
]
.footnote[See [all of the options](https://codex.wordpress.org/Class_Reference/WP_Query#Pagination_Parameters) in the Codex.]
---
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### Common Uses
### Creating a Custom Query
### Common Parameters
### Parameters to avoid
### Functions to avoid
]
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* `get_posts()`
* `query_posts()`
]
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### Common Uses
### Creating a Custom Query
### Common Parameters
### Parameters to avoid
### Functions to avoid
### Caching
]
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* **NEVER** Cache a `WP_Query` object itself!
* For more than a handful of posts, cache the IDs.

```php
$ids = get_transient( 'custom-ids' );
if ( false === $ids ) {
		$ids = array( 0 );
		$query = new WP_Query( array(
			'posts_per_page'         => 20,
			'no_found_rows'          => true,
			'fields'                 => 'ids',
			'update_post_meta_cache' => false,
			'update_post_term_cache' => false,
			'ignore_sticky_posts'    => true,
		) );

if ( ! empty( $query->posts ) ) {
			$ids = $query->posts;
			set_transient( 'custom-ids', $ids, DAY_IN_SECONDS );
		}
}
$query = new WP_Query( array(
		'post__in'            => $ids,
		'orderby'             => 'post__in',
		'ignore_sticky_posts' => true,
) );

// Do whatever you would normally do with your query here
```
]
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## Advanced tips
]
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### `pre_get_posts`
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* Best way to modify queries before they are run.
* Should be used instead of `query_posts`

```php
// Set pagination to 20 posts per page.
add_action( 'pre_get_posts', 'jpry_pre_get_posts' );
function jpry_pre_get_posts( $query ) {
		if ( $query->is_main_query() && ! is_admin() ) {
			$query->set( 'posts_per_page', 20 );
		}
}
```
```php
function jpry_pre_get_posts( $query ) {
		if ( ! $query->is_main_query() || $query->is_admin || $query->is_singular ) {
			return;
		}

// Remove pagination
		$query->set( 'nopaging', true );
		$query->set( 'post_per_page', 50 );
		$query->set( 'no_found_rows', true );

// Order by menu_order
		$query->set( 'orderby', 'menu_order' );
		$query->set( 'order', 'ASC' );
}
```
]
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.left-column[
### `pre_get_posts`
### Special Queries
]
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* Taxonomy query

```php
$query = new WP_Query( array(
		'post_type' => 'post',
		'tax_query' => array(
			array(
				'taxonomy' => 'people',
				'field'    => 'slug',
				'terms'    => 'bob',
			),
		),
) );
```
* Meta query

```php
$query = new WP_Query( array(
		'post_type'  => 'post',
		'meta_key'   => 'color',
		'meta_value' => 'green',
) );
```
]
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### `pre_get_posts`
### Special Queries
]
.right-column[
* Search

```php
$query = new WP_Query( array(
		's' => 'term',
) );
```
]
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# Questions?

???

Questions to answer:
* Why is `wp_reset_postdata()` needed?
* When is `wp_reset_postdata()` needed?
* Do custom queries add any type of performance hit to the page load time?
 * Do I need to limit how much data is returned?
 * Is it better to return as much as possible and then parse it in memory?
* but I'm interested in using elastic search or other search methodologies and I believe manipulation of this function is part of that process

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## Jeremy Pry

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