Lets write a custom function to doctrine

Posted on Jan 27, 2022

Doctrine is well-known ORM for php applications, especially apps which uses #symfony framework. I like to use symfony when i need to write a php application in all scale.

Doctrine is fittest ORM for sql operation in #PHP ecosystem in my opinion. I want to talk about writing custom #dql functions for doctrine.

Often i have need to use native #postgresql functions in my apps, like json_equalityfunction that i created. I use that function like this json_equality(table.jsoncolumn,'fieldname_injsoncolumn','subfield_injsoncolumn') and it will generate that sql table.column -> 'fielname_injsoncolumn' ->> 'subfield_injsoncolumn' and the postgres will look json column for correct equation.

First, let’s understand how it works. But, i will not go deep, if you interested you can learn about what is AST.

Doctrine have a parser for queries, it will parse what you write as query and then it will convert everything to sql queries. So, its not same what you write in your php code with sql queries. For example;

$qb = $em->createQuery('SELECT u FROM App\Entity\User WHERE u.id = 3');
SELECT u FROM user u WHERE u.id=3

Look at the above. These two thing contains similar terms, SELECT , FROM,WHERE, maybe you are thinking these are same, but NOT. First ones are just like placeholders, they are DQL statements, orm will change everything inside the query to SQL statements.

Like this, when you write SELECT u FROM App\Entity\User WHERE json_equality(u.metadata,'social','allow_to_follow') = 1 query, doctrine will parse it and convert to that SELECT u FROM user u WHERE CAST (u.metadata -> 'social' ->> 'allow_to_follow' AS INTEGER) = 1 query.

i assume you know json operators on postgres, if not, you can read documentation

Ok. Let’s write some code.

We have to create JsonEquality class which extends from Doctrine\ORM\Query\AST\Functions\FunctionNode class and that class will be placed in src/Doctrine/ORM/Query/AST/Functions/JsonEquality.php file.

It will have two methods. First method name is parse and it will take one argument, its Doctrine\ORM\Query\Parser. We will use that argument to parse the part of the query. Second method name is getSql and it will take one argument, its Doctrine\ORM\Query\SqlWalker. We will use that argument to start parsing to part of query and will return part of the SQL query.

Also we need two properties on that class to store parsed values in parse method and then use those properties in getSql method. It will be private:

private $field;
private $json_fields=[];

In the parse method, we will parse the part of the DQL query. Variable name is $parser for argument of method. And this parser have a method named match it will wait for a token to match, and it will walk through on the query until next token match or node match (wtf is the node? you can read about AST, seriously!). Also there is a ton of methods to generate predefined tokens, like StringPrimary method for string matches, AritmeticExpression for more complex expressions and subqueries. There is also another method exists in Parser object.

We can write first section.

public function parse(Parser $parser)
	$parser->match(Lexer::T_IDENTIFIER); //its our identifier json_equality
	$this->field = $parser->StringPrimary(); //we are storing first argument of json_equality function as property. This is not the calue, its node of the first value. We will use that in getSql method.
	$parser->match(Lexer::T_COMMA); //this is the comma after first argument

Let’s stop here and think a little. Our function requires how many arguments? We saw three in example json_equality(table.userdata,'user','firstname') but it may be less; json_equality(table.userdata,'username') or it may be more; json_equality(table.userdata,'comments','counts','favorite'), then how we can handle dynamic lenght in arguments? There is no argument spreading feature in DQL. So? Maybe we can try another approach;

public function parse(Parser $parser)
	$this->field = $parser->StringPrimary();
	$lexer = $parser->getLexer(); //we will use it to look to the type of the current token
	while(count($this->json_fields)<1 || $lexer->lookahead['type'] != Lexer::T_CLOSE_PARENTHESIS) { //loop until reach the close paranthesis
     $parser->match(Lexer::T_COMMA); //walk over comma
     $this->json_fields[]= $parser->ArithmeticExpression(); //add new node to array property
	$parser->match(Lexer::T_CLOSE_PARENTHESIS);//walk over close parenthesis and complete the parsing

Thats it! Our parse method is done and also have dynamic sized argument support.

We can contunie to generate SQL code.

In the getSql method, we need just dispatch method of nodes. It will take value of the node and we will assign to variables, and we will use to generate SQL code.

//lets assume our dql is json_equality(table.userdata,'user','firstname')
public function getSql(SqlWalker $sqlWalker)
	$field = $this->field->dispatch($sqlWalker); //get value from node, it will be table.userdata
	$values = []; // it will store json fields

	for($i = 0; $i<count($this->json_fields); $i++){
	 $values[]=$this->json_fields[$i]->dispatch($sqlWalker); // we have to dispatch all fields and push values to $values array
	$lastValue= array_pop($values); //we are cutting the last element of the values array. We will use that just after ->> oparator, others will be use -> operator. 
	 $json = join(' -> ',$values).' ->> '.$lastValue;
	 $json = array_pop($values).' ->> '.$lastValue;

	//and return generated SQL. In here i create for integer values, you can make it works for your needs. 
	return sprintf(
	 'CAST (%s -> %s AS INTEGER)', $field, $json

Cool, right? But wait! How can use it?

It must be registered in config/packages/doctrine.yaml file, or you can register via php for non-symfony apps. Check the documentation.

	  json_equality: 'App\Doctrine\ORM\Query\AST\Functions\JsonEquality'

Now you can use it in your code.

$qb = $this->createQueryBuilder('u');
$qb->andWhere("json_equality(u.metadata,'social','follow_count') = 100");
echo $qb->getQuery()->getSQL();

And the result;

SELECT * FROM user WHERE CAST( u.metadata -> 'social' ->> 'follow_count' AS INTEGER) = 100;

Happy coding!

#php #symfony #english #web #doctrine

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