MDL-76902 reportbuilder: entity method for defining table join alias.

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
      *