From 3ca41c77e4373ae8e9653db9d0d12b520c8eb02c Mon Sep 17 00:00:00 2001
From: Paul Holden <paulh@moodle.com>
Date: Tue, 17 Jan 2023 11:02:41 +0000
Subject: [PATCH] MDL-76902 reportbuilder: entity method for defining table
 join alias.

---
 reportbuilder/classes/local/entities/base.php | 30 ++++++++++++++++++-
 .../tests/local/entities/base_test.php        | 21 +++++++++++++
 reportbuilder/upgrade.txt                     |  1 +
 3 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/reportbuilder/classes/local/entities/base.php b/reportbuilder/classes/local/entities/base.php
index 1dfcacefe94..29a56665547 100644
--- a/reportbuilder/classes/local/entities/base.php
+++ b/reportbuilder/classes/local/entities/base.php
@@ -38,9 +38,12 @@ abstract class base {
     /** @var lang_string $entitytitle Used as a title for the entity in reports */
     private $entitytitle = null;
 
-    /** @var array $tablealiases Database tables that this entity uses and their default aliases */
+    /** @var array $tablealiases Database tables that this entity uses and their aliases */
     private $tablealiases = [];
 
+    /** @var array $tablejoinaliases Database tables that have already been joined to the report and their aliases */
+    private $tablejoinaliases = [];
+
     /** @var string[] $joins List of SQL joins for the entity */
     private $joins = [];
 
@@ -182,6 +185,31 @@ abstract class base {
         return $this->tablealiases[$tablename] ?? $defaulttablealiases[$tablename];
     }
 
+    /**
+     * Set the alias for given database table that has already been added to the report. Enables entities to avoid additional
+     * joins on the same table by allowing re-use of existing table aliases in their own queries, {@see has_table_join_alias}
+     *
+     * @param string $tablename
+     * @param string $alias
+     * @return self
+     */
+    final public function set_table_join_alias(string $tablename, string $alias): self {
+        $this->tablejoinaliases[$tablename] = $alias;
+
+        // Internally set the same table alias for the entity.
+        return $this->set_table_alias($tablename, $alias);
+    }
+
+    /**
+     * Determine whether defined table join alias was specified. Call {@see get_table_alias} to retrieve said value
+     *
+     * @param string $tablename
+     * @return bool
+     */
+    final public function has_table_join_alias(string $tablename): bool {
+        return array_key_exists($tablename, $this->tablejoinaliases);
+    }
+
     /**
      * Add join clause required for this entity to join to existing tables/entities
      *
diff --git a/reportbuilder/tests/local/entities/base_test.php b/reportbuilder/tests/local/entities/base_test.php
index a4110934997..38e9ff784a8 100644
--- a/reportbuilder/tests/local/entities/base_test.php
+++ b/reportbuilder/tests/local/entities/base_test.php
@@ -114,6 +114,27 @@ class base_test extends advanced_testcase {
         ]);
     }
 
+    /**
+     * Test setting table join alias
+     */
+    public function test_set_table_join_alias(): void {
+        $entity = new base_test_entity();
+
+        $entity->set_table_join_alias('mytable', 'newalias');
+        $this->assertTrue($entity->has_table_join_alias('mytable'));
+        $this->assertEquals('newalias', $entity->get_table_alias('mytable'));
+    }
+
+    /**
+     * Test that entity doesn't have table join alias by default
+     *
+     * {@see test_set_table_join_alias} for assertion where it does
+     */
+    public function test_has_table_join_alias(): void {
+        $entity = new base_test_entity();
+        $this->assertFalse($entity->has_table_join_alias('mytable'));
+    }
+
     /**
      * Test entity name
      */
diff --git a/reportbuilder/upgrade.txt b/reportbuilder/upgrade.txt
index 410ebc3d168..66acedccacf 100644
--- a/reportbuilder/upgrade.txt
+++ b/reportbuilder/upgrade.txt
@@ -7,6 +7,7 @@ Information provided here is intended especially for developers.
   - `core_reportbuilder_can_view_system_report`
   - `core_reportbuilder_retrieve_system_report`
 * New `get_tag_joins_for_entity` helper in base entity class, for returning SQL joins necessary for retrieving tags
+* New methods `[set|has]_table_join_alias` in the base entity class, to allow entities to reduce joins on the same table
 * New `set_is_deprecated` method in base `local\report\[column|filter]` classes to deprecate report entity columns and filters
 * The following report entity columns have been deprecated, with replacements as follows:
   - `comment:context` => `context:name`