The class creates the JOIN and WHERE parts of the SQL query, which, in addition to the main query, will filter the result by the specified terms (taxonomy elements).
WP_Tax_Query is a helper that allows main classes, such as WP_Query, to filter results by taxonomy elements (terms). It generates sub-queries JOIN and WHERE. The resulting parts of the SQL queries are then added to the main query.
To build a query for terms, at least 2 tables need to be joined:
JOIN wp_term_relationships + JOIN wp_term_taxonomy - when we query by term IDs.
JOIN wp_term_relationships + JOIN wp_term_taxonomy + JOIN wp_terms - when we query by term slugs.
Thus, multiple JOINs significantly slow down the query, especially if there are many posts in the main table.
This class uses WP_Term_Query for pre-processing parameters. So, when we specify a term slug in the query, this slug is converted to term_taxonomy_id, which in turn allows the use of only one JOIN - JOIN wp_term_relationships. And since WP_Term_Query caches term IDs, when using persistent caching, WP_Term_Query does not make any queries to the database at all, which further speeds up the selection.
$tax_query is an array where each element is an array with parameters of a separate query, i.e., it is an array of arrays. This structure allows creating multiple queries. Here’s how it looks:
Parameters for the taxonomy query. See WP_Tax_Query::__construct(). Can accept the following series of nested arguments:
relation(string)
How to select posts from the specified taxonomies. Can be:
AND - posts that belong to all specified taxonomy terms.
OR - posts that belong to any of the specified taxonomy terms.
Default: AND
Specified in the first array, and terms in the nested arrays, which can have the following parameters:
taxonomy(string)
Name of the taxonomy.
field(string)
Field that will be specified in the terms parameter. Can be:
id or term_id - in terms we specify term IDs.
name - in terms we specify the term title.
slug - in terms we specify the term slug.
Default: 'term_id'
terms(number/string/array)
Taxonomy terms from which to retrieve posts.
operator(string)
Operator indicating how to compare the specified terms in the terms parameter. Can be:
IN - posts from the specified terms (default).
NOT IN - posts from all terms except the specified ones.
AND - posts belonging to all specified terms.
EXISTS - posts from the taxonomy (that have any taxonomy term). In this case, the terms parameter does not need to be specified. Since version 4.1.
NOT EXISTS - posts NOT from the taxonomy (that do not have any taxonomy term). In this case, the terms parameter does not need to be specified. Since version 4.1.
Default: 'IN'
include_children(boolean)
Whether to include posts from child terms (for hierarchical taxonomies). true - include. Default: true
tax_query is an array, the elements of which are other arrays, each specifying the taxonomy, its terms, and how to use those terms. The relation operator is specified in the first array of tax_query and determines how to compare the nested arrays with each other. This structure allows creating a query to multiple taxonomies simultaneously.
#1 Generate the join and where parts of the SQL query
$tax_query = [
[
'taxonomy' => 'coincat',
'terms' => [ 610, 544 ],
'field' => 'term_id',
'include_children' => 1,
]
];
$taxquery = new WP_TAX_Query( $tax_query );
$sql = $taxquery->get_sql( 'my_table', 'main_id' );
/* $sql will contain the following array:
Array(
[join] => LEFT JOIN wp_term_relationships ON (my_table.main_id = wp_term_relationships.object_id)
[where] => AND ( wp_term_relationships.term_taxonomy_id IN (544,610) )
)
*/
The specified terms 610, 544 must exist. Before creating the query, the class checks the actual presence of these terms in the database.
/* If the term with ID 610 does not exist, then the result will be:
Array(
[join] =>
[where] => AND (0 = 1)
)
*/
/* The term with ID 610 does not exist, while 544 exists, with 'relation' => 'OR':
Array
(
[join] => LEFT JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id)
[where] => AND ( wp_term_relationships.term_taxonomy_id IN (544) )
)
*/
/* The term with ID 610 does not exist, while 544 exists, with 'relation' => 'AND':
Array
(
[join] => LEFT JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id)
[where] => AND ( wp_term_relationships.term_taxonomy_id IN (544) )
)
The same as with 'relation' => 'OR', although you might expect [where] => AND (0 = 1)
*/
If you specify slugs, then the resulting query will include all the same term IDs:
class WP_Tax_Query {
/**
* Array of taxonomy queries.
*
* See WP_Tax_Query::__construct() for information on tax query arguments.
*
* @since 3.1.0
* @var array
*/
public $queries = array();
/**
* The relation between the queries. Can be one of 'AND' or 'OR'.
*
* @since 3.1.0
* @var string
*/
public $relation;
/**
* Standard response when the query should not return any rows.
*
* @since 3.2.0
* @var string
*/
private static $no_results = array(
'join' => array( '' ),
'where' => array( '0 = 1' ),
);
/**
* A flat list of table aliases used in the JOIN clauses.
*
* @since 4.1.0
* @var array
*/
protected $table_aliases = array();
/**
* Terms and taxonomies fetched by this query.
*
* We store this data in a flat array because they are referenced in a
* number of places by WP_Query.
*
* @since 4.1.0
* @var array
*/
public $queried_terms = array();
/**
* Database table that where the metadata's objects are stored (eg $wpdb->users).
*
* @since 4.1.0
* @var string
*/
public $primary_table;
/**
* Column in 'primary_table' that represents the ID of the object.
*
* @since 4.1.0
* @var string
*/
public $primary_id_column;
/**
* Constructor.
*
* @since 3.1.0
* @since 4.1.0 Added support for `$operator` 'NOT EXISTS' and 'EXISTS' values.
*
* @param array $tax_query {
* Array of taxonomy query clauses.
*
* @type string $relation Optional. The MySQL keyword used to join
* the clauses of the query. Accepts 'AND', or 'OR'. Default 'AND'.
* @type array ...$0 {
* An array of first-order clause parameters, or another fully-formed tax query.
*
* @type string $taxonomy Taxonomy being queried. Optional when field=term_taxonomy_id.
* @type string|int|array $terms Term or terms to filter by.
* @type string $field Field to match $terms against. Accepts 'term_id', 'slug',
* 'name', or 'term_taxonomy_id'. Default: 'term_id'.
* @type string $operator MySQL operator to be used with $terms in the WHERE clause.
* Accepts 'AND', 'IN', 'NOT IN', 'EXISTS', 'NOT EXISTS'.
* Default: 'IN'.
* @type bool $include_children Optional. Whether to include child terms.
* Requires a $taxonomy. Default: true.
* }
* }
*/
public function __construct( $tax_query ) {
if ( isset( $tax_query['relation'] ) ) {
$this->relation = $this->sanitize_relation( $tax_query['relation'] );
} else {
$this->relation = 'AND';
}
$this->queries = $this->sanitize_query( $tax_query );
}
/**
* Ensures the 'tax_query' argument passed to the class constructor is well-formed.
*
* Ensures that each query-level clause has a 'relation' key, and that
* each first-order clause contains all the necessary keys from `$defaults`.
*
* @since 4.1.0
*
* @param array $queries Array of queries clauses.
* @return array Sanitized array of query clauses.
*/
public function sanitize_query( $queries ) {
$cleaned_query = array();
$defaults = array(
'taxonomy' => '',
'terms' => array(),
'field' => 'term_id',
'operator' => 'IN',
'include_children' => true,
);
foreach ( $queries as $key => $query ) {
if ( 'relation' === $key ) {
$cleaned_query['relation'] = $this->sanitize_relation( $query );
// First-order clause.
} elseif ( self::is_first_order_clause( $query ) ) {
$cleaned_clause = array_merge( $defaults, $query );
$cleaned_clause['terms'] = (array) $cleaned_clause['terms'];
$cleaned_query[] = $cleaned_clause;
/*
* Keep a copy of the clause in the flate
* $queried_terms array, for use in WP_Query.
*/
if ( ! empty( $cleaned_clause['taxonomy'] ) && 'NOT IN' !== $cleaned_clause['operator'] ) {
$taxonomy = $cleaned_clause['taxonomy'];
if ( ! isset( $this->queried_terms[ $taxonomy ] ) ) {
$this->queried_terms[ $taxonomy ] = array();
}
/*
* Backward compatibility: Only store the first
* 'terms' and 'field' found for a given taxonomy.
*/
if ( ! empty( $cleaned_clause['terms'] ) && ! isset( $this->queried_terms[ $taxonomy ]['terms'] ) ) {
$this->queried_terms[ $taxonomy ]['terms'] = $cleaned_clause['terms'];
}
if ( ! empty( $cleaned_clause['field'] ) && ! isset( $this->queried_terms[ $taxonomy ]['field'] ) ) {
$this->queried_terms[ $taxonomy ]['field'] = $cleaned_clause['field'];
}
}
// Otherwise, it's a nested query, so we recurse.
} elseif ( is_array( $query ) ) {
$cleaned_subquery = $this->sanitize_query( $query );
if ( ! empty( $cleaned_subquery ) ) {
// All queries with children must have a relation.
if ( ! isset( $cleaned_subquery['relation'] ) ) {
$cleaned_subquery['relation'] = 'AND';
}
$cleaned_query[] = $cleaned_subquery;
}
}
}
return $cleaned_query;
}
/**
* Sanitizes a 'relation' operator.
*
* @since 4.1.0
*
* @param string $relation Raw relation key from the query argument.
* @return string Sanitized relation. Either 'AND' or 'OR'.
*/
public function sanitize_relation( $relation ) {
if ( 'OR' === strtoupper( $relation ) ) {
return 'OR';
} else {
return 'AND';
}
}
/**
* Determines whether a clause is first-order.
*
* A "first-order" clause is one that contains any of the first-order
* clause keys ('terms', 'taxonomy', 'include_children', 'field',
* 'operator'). An empty clause also counts as a first-order clause,
* for backward compatibility. Any clause that doesn't meet this is
* determined, by process of elimination, to be a higher-order query.
*
* @since 4.1.0
*
* @param array $query Tax query arguments.
* @return bool Whether the query clause is a first-order clause.
*/
protected static function is_first_order_clause( $query ) {
return is_array( $query ) && ( empty( $query ) || array_key_exists( 'terms', $query ) || array_key_exists( 'taxonomy', $query ) || array_key_exists( 'include_children', $query ) || array_key_exists( 'field', $query ) || array_key_exists( 'operator', $query ) );
}
/**
* Generates SQL clauses to be appended to a main query.
*
* @since 3.1.0
*
* @param string $primary_table Database table where the object being filtered is stored (eg wp_users).
* @param string $primary_id_column ID column for the filtered object in $primary_table.
* @return string[] {
* Array containing JOIN and WHERE SQL clauses to append to the main query.
*
* @type string $join SQL fragment to append to the main JOIN clause.
* @type string $where SQL fragment to append to the main WHERE clause.
* }
*/
public function get_sql( $primary_table, $primary_id_column ) {
$this->primary_table = $primary_table;
$this->primary_id_column = $primary_id_column;
return $this->get_sql_clauses();
}
/**
* Generates SQL clauses to be appended to a main query.
*
* Called by the public WP_Tax_Query::get_sql(), this method
* is abstracted out to maintain parity with the other Query classes.
*
* @since 4.1.0
*
* @return string[] {
* Array containing JOIN and WHERE SQL clauses to append to the main query.
*
* @type string $join SQL fragment to append to the main JOIN clause.
* @type string $where SQL fragment to append to the main WHERE clause.
* }
*/
protected function get_sql_clauses() {
/*
* $queries are passed by reference to get_sql_for_query() for recursion.
* To keep $this->queries unaltered, pass a copy.
*/
$queries = $this->queries;
$sql = $this->get_sql_for_query( $queries );
if ( ! empty( $sql['where'] ) ) {
$sql['where'] = ' AND ' . $sql['where'];
}
return $sql;
}
/**
* Generates SQL clauses for a single query array.
*
* If nested subqueries are found, this method recurses the tree to
* produce the properly nested SQL.
*
* @since 4.1.0
*
* @param array $query Query to parse (passed by reference).
* @param int $depth Optional. Number of tree levels deep we currently are.
* Used to calculate indentation. Default 0.
* @return string[] {
* Array containing JOIN and WHERE SQL clauses to append to a single query array.
*
* @type string $join SQL fragment to append to the main JOIN clause.
* @type string $where SQL fragment to append to the main WHERE clause.
* }
*/
protected function get_sql_for_query( &$query, $depth = 0 ) {
$sql_chunks = array(
'join' => array(),
'where' => array(),
);
$sql = array(
'join' => '',
'where' => '',
);
$indent = '';
for ( $i = 0; $i < $depth; $i++ ) {
$indent .= ' ';
}
foreach ( $query as $key => &$clause ) {
if ( 'relation' === $key ) {
$relation = $query['relation'];
} elseif ( is_array( $clause ) ) {
// This is a first-order clause.
if ( $this->is_first_order_clause( $clause ) ) {
$clause_sql = $this->get_sql_for_clause( $clause, $query );
$where_count = count( $clause_sql['where'] );
if ( ! $where_count ) {
$sql_chunks['where'][] = '';
} elseif ( 1 === $where_count ) {
$sql_chunks['where'][] = $clause_sql['where'][0];
} else {
$sql_chunks['where'][] = '( ' . implode( ' AND ', $clause_sql['where'] ) . ' )';
}
$sql_chunks['join'] = array_merge( $sql_chunks['join'], $clause_sql['join'] );
// This is a subquery, so we recurse.
} else {
$clause_sql = $this->get_sql_for_query( $clause, $depth + 1 );
$sql_chunks['where'][] = $clause_sql['where'];
$sql_chunks['join'][] = $clause_sql['join'];
}
}
}
// Filter to remove empties.
$sql_chunks['join'] = array_filter( $sql_chunks['join'] );
$sql_chunks['where'] = array_filter( $sql_chunks['where'] );
if ( empty( $relation ) ) {
$relation = 'AND';
}
// Filter duplicate JOIN clauses and combine into a single string.
if ( ! empty( $sql_chunks['join'] ) ) {
$sql['join'] = implode( ' ', array_unique( $sql_chunks['join'] ) );
}
// Generate a single WHERE clause with proper brackets and indentation.
if ( ! empty( $sql_chunks['where'] ) ) {
$sql['where'] = '( ' . "\n " . $indent . implode( ' ' . "\n " . $indent . $relation . ' ' . "\n " . $indent, $sql_chunks['where'] ) . "\n" . $indent . ')';
}
return $sql;
}
/**
* Generates SQL JOIN and WHERE clauses for a "first-order" query clause.
*
* @since 4.1.0
*
* @global wpdb $wpdb The WordPress database abstraction object.
*
* @param array $clause Query clause (passed by reference).
* @param array $parent_query Parent query array.
* @return array {
* Array containing JOIN and WHERE SQL clauses to append to a first-order query.
*
* @type string[] $join Array of SQL fragments to append to the main JOIN clause.
* @type string[] $where Array of SQL fragments to append to the main WHERE clause.
* }
*/
public function get_sql_for_clause( &$clause, $parent_query ) {
global $wpdb;
$sql = array(
'where' => array(),
'join' => array(),
);
$join = '';
$where = '';
$this->clean_query( $clause );
if ( is_wp_error( $clause ) ) {
return self::$no_results;
}
$terms = $clause['terms'];
$operator = strtoupper( $clause['operator'] );
if ( 'IN' === $operator ) {
if ( empty( $terms ) ) {
return self::$no_results;
}
$terms = implode( ',', $terms );
/*
* Before creating another table join, see if this clause has a
* sibling with an existing join that can be shared.
*/
$alias = $this->find_compatible_table_alias( $clause, $parent_query );
if ( false === $alias ) {
$i = count( $this->table_aliases );
$alias = $i ? 'tt' . $i : $wpdb->term_relationships;
// Store the alias as part of a flat array to build future iterators.
$this->table_aliases[] = $alias;
// Store the alias with this clause, so later siblings can use it.
$clause['alias'] = $alias;
$join .= " LEFT JOIN $wpdb->term_relationships";
$join .= $i ? " AS $alias" : '';
$join .= " ON ($this->primary_table.$this->primary_id_column = $alias.object_id)";
}
$where = "$alias.term_taxonomy_id $operator ($terms)";
} elseif ( 'NOT IN' === $operator ) {
if ( empty( $terms ) ) {
return $sql;
}
$terms = implode( ',', $terms );
$where = "$this->primary_table.$this->primary_id_column NOT IN (
SELECT object_id
FROM $wpdb->term_relationships
WHERE term_taxonomy_id IN ($terms)
)";
} elseif ( 'AND' === $operator ) {
if ( empty( $terms ) ) {
return $sql;
}
$num_terms = count( $terms );
$terms = implode( ',', $terms );
$where = "(
SELECT COUNT(1)
FROM $wpdb->term_relationships
WHERE term_taxonomy_id IN ($terms)
AND object_id = $this->primary_table.$this->primary_id_column
) = $num_terms";
} elseif ( 'NOT EXISTS' === $operator || 'EXISTS' === $operator ) {
$where = $wpdb->prepare(
"$operator (
SELECT 1
FROM $wpdb->term_relationships
INNER JOIN $wpdb->term_taxonomy
ON $wpdb->term_taxonomy.term_taxonomy_id = $wpdb->term_relationships.term_taxonomy_id
WHERE $wpdb->term_taxonomy.taxonomy = %s
AND $wpdb->term_relationships.object_id = $this->primary_table.$this->primary_id_column
)",
$clause['taxonomy']
);
}
$sql['join'][] = $join;
$sql['where'][] = $where;
return $sql;
}
/**
* Identifies an existing table alias that is compatible with the current query clause.
*
* We avoid unnecessary table joins by allowing each clause to look for
* an existing table alias that is compatible with the query that it
* needs to perform.
*
* An existing alias is compatible if (a) it is a sibling of `$clause`
* (ie, it's under the scope of the same relation), and (b) the combination
* of operator and relation between the clauses allows for a shared table
* join. In the case of WP_Tax_Query, this only applies to 'IN'
* clauses that are connected by the relation 'OR'.
*
* @since 4.1.0
*
* @param array $clause Query clause.
* @param array $parent_query Parent query of $clause.
* @return string|false Table alias if found, otherwise false.
*/
protected function find_compatible_table_alias( $clause, $parent_query ) {
$alias = false;
// Confidence check. Only IN queries use the JOIN syntax.
if ( ! isset( $clause['operator'] ) || 'IN' !== $clause['operator'] ) {
return $alias;
}
// Since we're only checking IN queries, we're only concerned with OR relations.
if ( ! isset( $parent_query['relation'] ) || 'OR' !== $parent_query['relation'] ) {
return $alias;
}
$compatible_operators = array( 'IN' );
foreach ( $parent_query as $sibling ) {
if ( ! is_array( $sibling ) || ! $this->is_first_order_clause( $sibling ) ) {
continue;
}
if ( empty( $sibling['alias'] ) || empty( $sibling['operator'] ) ) {
continue;
}
// The sibling must both have compatible operator to share its alias.
if ( in_array( strtoupper( $sibling['operator'] ), $compatible_operators, true ) ) {
$alias = preg_replace( '/\W/', '_', $sibling['alias'] );
break;
}
}
return $alias;
}
/**
* Validates a single query.
*
* @since 3.2.0
*
* @param array $query The single query. Passed by reference.
*/
private function clean_query( &$query ) {
if ( empty( $query['taxonomy'] ) ) {
if ( 'term_taxonomy_id' !== $query['field'] ) {
$query = new WP_Error( 'invalid_taxonomy', __( 'Invalid taxonomy.' ) );
return;
}
// So long as there are shared terms, 'include_children' requires that a taxonomy is set.
$query['include_children'] = false;
} elseif ( ! taxonomy_exists( $query['taxonomy'] ) ) {
$query = new WP_Error( 'invalid_taxonomy', __( 'Invalid taxonomy.' ) );
return;
}
if ( 'slug' === $query['field'] || 'name' === $query['field'] ) {
$query['terms'] = array_unique( (array) $query['terms'] );
} else {
$query['terms'] = wp_parse_id_list( $query['terms'] );
}
if ( is_taxonomy_hierarchical( $query['taxonomy'] ) && $query['include_children'] ) {
$this->transform_query( $query, 'term_id' );
if ( is_wp_error( $query ) ) {
return;
}
$children = array();
foreach ( $query['terms'] as $term ) {
$children = array_merge( $children, get_term_children( $term, $query['taxonomy'] ) );
$children[] = $term;
}
$query['terms'] = $children;
}
$this->transform_query( $query, 'term_taxonomy_id' );
}
/**
* Transforms a single query, from one field to another.
*
* Operates on the `$query` object by reference. In the case of error,
* `$query` is converted to a WP_Error object.
*
* @since 3.2.0
*
* @param array $query The single query. Passed by reference.
* @param string $resulting_field The resulting field. Accepts 'slug', 'name', 'term_taxonomy_id',
* or 'term_id'. Default 'term_id'.
*/
public function transform_query( &$query, $resulting_field ) {
if ( empty( $query['terms'] ) ) {
return;
}
if ( $query['field'] === $resulting_field ) {
return;
}
$resulting_field = sanitize_key( $resulting_field );
// Empty 'terms' always results in a null transformation.
$terms = array_filter( $query['terms'] );
if ( empty( $terms ) ) {
$query['terms'] = array();
$query['field'] = $resulting_field;
return;
}
$args = array(
'get' => 'all',
'number' => 0,
'taxonomy' => $query['taxonomy'],
'update_term_meta_cache' => false,
'orderby' => 'none',
);
// Term query parameter name depends on the 'field' being searched on.
switch ( $query['field'] ) {
case 'slug':
$args['slug'] = $terms;
break;
case 'name':
$args['name'] = $terms;
break;
case 'term_taxonomy_id':
$args['term_taxonomy_id'] = $terms;
break;
default:
$args['include'] = wp_parse_id_list( $terms );
break;
}
if ( ! is_taxonomy_hierarchical( $query['taxonomy'] ) ) {
$args['number'] = count( $terms );
}
$term_query = new WP_Term_Query();
$term_list = $term_query->query( $args );
if ( is_wp_error( $term_list ) ) {
$query = $term_list;
return;
}
if ( 'AND' === $query['operator'] && count( $term_list ) < count( $query['terms'] ) ) {
$query = new WP_Error( 'inexistent_terms', __( 'Inexistent terms.' ) );
return;
}
$query['terms'] = wp_list_pluck( $term_list, $resulting_field );
$query['field'] = $resulting_field;
}
}