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Adding ability to detect inheritance relationships between tables
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‎README.md‎

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@@ -47,6 +47,28 @@ A **junction table** is a table:
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- that has **exactly 2 foreign keys**
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- that has **only 2 columns** (or **3 columns** if the one of those is an *autoincremented primary key*).
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## Detecting inheritance relationship between tables
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### About inheritance relationships
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If a table "user" has a primary key that is also a foreign key pointing on table "contact", then table "user" is
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considered to be a child of table "contact". This is because you cannot create a row in "user" without having a row
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with the same ID in "contact".
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Therefore, a "user" ID has to match a "contact", but a "contact" has not necessarily a "user" associated.
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### Detecting inheritance relationships
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You can use `SchemaAnalyzer` to detect parent / child relationships.
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```php
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$parent = $schemaAnalyzer->getParentTable("user");
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// This will return the "contact" table (as a string)
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$children = $schemaAnalyzer->getChildrenTables("contact");
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// This will return an array of tables whose parent is contact: ["user"]
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```
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## Computing the shortest path between 2 tables
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Following foreign keys, the `getShortestPath` function will try to find the shortest path between 2 tables.
@@ -56,6 +78,8 @@ Internals:
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- Each foreign key has a *cost* of 1
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- Junction tables have a *cost* of 1.5, instead of 2 (one for each foreign key)
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- Foreign keys representing an inheritance relationship (i.e. foreign keys binding the primary keys of 2 tables)
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have a *cost* of 0.1
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```php
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// $conn is the DBAL connection.

‎src/SchemaAnalyzer.php‎

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@@ -22,6 +22,7 @@
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class SchemaAnalyzer
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{
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private static $WEIGHT_FK = 1;
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private static $WEIGHT_INHERITANCE_FK = 0.1;
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private static $WEIGHT_JOINTURE_TABLE = 1.5;
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const WEIGHT_IMPORTANT = 0.75;
@@ -124,7 +125,11 @@ private function isJunctionTable(Table $table)
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return false;
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}
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$pkColumns = $table->getPrimaryKeyColumns();
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if ($table->hasPrimaryKey()) {
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$pkColumns = $table->getPrimaryKeyColumns();
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} else {
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$pkColumns = [];
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}
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if (count($pkColumns) == 1 && count($columns) == 2) {
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return false;
@@ -257,6 +262,8 @@ private function buildSchemaGraph()
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$edge = $graph->getVertex($table->getName())->createEdge($graph->getVertex($fk->getForeignTableName()));
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if (isset($this->alteredCosts[$fk->getLocalTable()->getName()][implode(',',$fk->getLocalColumns())])) {
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$cost = $this->alteredCosts[$fk->getLocalTable()->getName()][implode(',',$fk->getLocalColumns())];
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} elseif ($this->isInheritanceRelationship($fk)) {
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$cost = self::$WEIGHT_INHERITANCE_FK;
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} else {
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$cost = self::$WEIGHT_FK;
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}
@@ -421,4 +428,103 @@ public function setTableCostModifiers(array $tableCosts) {
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public function setForeignKeyCosts(array $fkCosts) {
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$this->alteredCosts = $fkCosts;
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}
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/**
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* Returns true if this foreign key represents an inheritance relationship,
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* i.e. if this foreign key is based on a primary key.
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* @param ForeignKeyConstraint $fk
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* @return true
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*/
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private function isInheritanceRelationship(ForeignKeyConstraint $fk) {
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if (!$fk->getLocalTable()->hasPrimaryKey()) {
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return false;
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}
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$fkColumnNames = $fk->getLocalColumns();
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$pkColumnNames = $fk->getLocalTable()->getPrimaryKeyColumns();
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sort($fkColumnNames);
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sort($pkColumnNames);
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return $fkColumnNames == $pkColumnNames;
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}
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/**
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* If this table is pointing to a parent table (if its primary key is a foreign key pointing on another table),
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* this function will return the pointed table.
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* This function will return null if there is no parent table.
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*
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* @param string $tableName
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* @return string|null
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*/
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public function getParentTable($tableName) {
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$cacheKey = $this->cachePrefix.'_parent_'.$tableName;
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$parent = $this->cache->fetch($cacheKey);
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if ($parent === false) {
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$parent = $this->getParentTableWithoutCache($tableName);
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$this->cache->save($cacheKey, $parent);
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}
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return $parent;
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}
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/**
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* If this table is pointing to a parent table (if its primary key is a foreign key pointing on another table),
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* this function will return the pointed table.
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* This function will return null if there is no parent table.
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*
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* @param string $tableName
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* @return string|null
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*/
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private function getParentTableWithoutCache($tableName) {
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$table = $this->getSchema()->getTable($tableName);
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foreach ($table->getForeignKeys() as $fk) {
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if ($this->isInheritanceRelationship($fk)) {
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return $fk->getForeignTableName();
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}
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}
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return null;
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}
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/**
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* If this table is pointed by children tables (if other child tables have a primary key that is also a
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* foreign key to this table), this function will return the list of child tables.
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* This function will return an empty array if there are no children tables.
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*
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* @param string $tableName
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* @return string[]
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*/
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public function getChildrenTables($tableName) {
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$cacheKey = $this->cachePrefix.'_children_'.$tableName;
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$parent = $this->cache->fetch($cacheKey);
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if ($parent === false) {
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$parent = $this->getChildrenTablesWithoutCache($tableName);
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$this->cache->save($cacheKey, $parent);
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}
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return $parent;
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}
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/**
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* If this table is pointed by children tables (if other child tables have a primary key that is also a
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* foreign key to this table), this function will return the list of child tables.
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* This function will return an empty array if there are no children tables.
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*
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* @param string $tableName
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* @return string[]
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*/
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private function getChildrenTablesWithoutCache($tableName) {
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$schema = $this->getSchema();
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$children = [];
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foreach ($schema->getTables() as $table) {
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if ($table->getName() === $tableName) {
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continue;
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}
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foreach ($table->getForeignKeys() as $fk) {
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if ($fk->getForeignTableName() === $tableName && $this->isInheritanceRelationship($fk)) {
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$children[] = $fk->getLocalTableName();
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}
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}
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}
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return $children;
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}
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}

‎tests/SchemaAnalyzerTest.php‎

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@@ -161,6 +161,24 @@ public function testJointureTableDetectionWith2ColumnsWith2FkOnOneCol() {
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$this->assertCount(0, $junctionTables);
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}
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public function testJointureTableDetectionWith2ColumnsAndNoPrimaryKey() {
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$schema = $this->getBaseSchema();
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$schema->getTable('role')->addColumn('right_id', 'integer');
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$role_right = $schema->createTable("role_right");
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$role_right->addColumn("role_id", "integer", array("unsigned" => true));
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$role_right->addColumn("right_id", "integer", array("unsigned" => true));
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$role_right->addForeignKeyConstraint($schema->getTable('role'), array("role_id"), array("id"), array("onUpdate" => "CASCADE"));
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$role_right->addForeignKeyConstraint($schema->getTable('right'), array("right_id"), array("id"), array("onUpdate" => "CASCADE"));
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$schemaAnalyzer = new SchemaAnalyzer(new StubSchemaManager($schema));
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$junctionTables = $schemaAnalyzer->detectJunctionTables();
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$this->assertCount(1, $junctionTables);
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}
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public function testJointureTableDetectionWith3ColumnsWithPkIsFk() {
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$schema = $this->getBaseSchema();
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@@ -411,5 +429,35 @@ public function testAmbiguityExceptionWithJointureAndModifiedWeight2() {
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$this->assertEquals("right", $fks[1]->getForeignTableName());
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}
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public function testInheritanceRelationship() {
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$schema = new Schema();
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$contact = $schema->createTable("contact");
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$contact->addColumn("id", "integer", array("unsigned" => true));
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$contact->addColumn("name", "string", array("length" => 32));
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$contact->setPrimaryKey(["id"]);
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$user = $schema->createTable("user");
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$user->addColumn("id", "integer", array("unsigned" => true));
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$user->addColumn("contact_id", "integer", array("unsigned" => true));
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$user->addColumn("login", "string", array("length" => 32));
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$user->setPrimaryKey(["id"]);
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$user->addForeignKeyConstraint($contact, array("id"), array("id"), array("onUpdate" => "CASCADE"));
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$user->addForeignKeyConstraint($contact, array("contact_id"), array("id"), array("onUpdate" => "CASCADE"));
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$schemaAnalyzer = new SchemaAnalyzer(new StubSchemaManager($schema));
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// No ambiguity exception should be thrown because we go through inheritance relationship first.
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$fks = $schemaAnalyzer->getShortestPath("user", "contact");
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$this->assertCount(1, $fks);
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$this->assertEquals("id", $fks[0]->getLocalColumns()[0]);
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$this->assertEquals('contact', $schemaAnalyzer->getParentTable('user'));
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$this->assertNull($schemaAnalyzer->getParentTable('contact'));
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$this->assertEquals(['user'], $schemaAnalyzer->getChildrenTables('contact'));
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$this->assertEquals([], $schemaAnalyzer->getChildrenTables('user'));
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}
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}
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