.. php:class:: Expression
Expression class implements a flexible way for you to define any custom expression then execute it as-is or as a part of another query or expression. Expression is supported anywhere in DSQL to allow you to express SQL syntax properly.
Quick Example:
$query->where('time', $query->expr(
'between "[]" and "[]"',
[$from_time, $to_time]
));
// Produces: .. where `time` between :a and :b
Another use of expression is to supply field instead of value and vice versa:
$query->where($query->expr(
'[] between time_from and time_to',
[$time]
));
// Produces: where :a between time_from and time_to
Yet another curious use for the DSQL library is if you have certain object in your ORM implementing :php:class:`Expressionable` interface. Then you can also use it within expressions:
$query->where($query->expr(
'[] between [] and []',
[$time, $model->getElement('time_form'), $model->getElement('time_to')]
));
// Produces: where :a between `time_from` and `time_to`
.. todo::
add more info or more precise example of Expressionable interface usage.
Another uses for expressions could be:
- Sub-Queries
- SQL functions, e.g. IF, CASE
- nested AND / OR clauses
- vendor-specific queries - "describe table"
- non-traditional constructions , UNIONS or SELECT INTO
Be careful when using those similar terms as they refer to different things:
- Properties refer to object properties, e.g. $expr->template, see :ref:`properties`
- Arguments refer to template arguments, e.g. select * from [table], see :ref:`expression-template`
- Parameters refer to the way of passing user values within a query where id=:a and are further explained below.
Because some values are un-safe to use in the query and can contain dangerous values they are kept outside of the SQL query string and are using PDO's bindParam instead. DSQL can consist of multiple objects and each object may have some parameters. During rendering those parameters are joined together to produce one complete query.
use Atk4\Data\Persistence\Sql\Expression;
$expr = new Expression("NOW()");
You can also use :php:meth:`expr()` method to create expression, in which case you do not have to define "use" block:
$query->where('time', '>', $query->expr('NOW()'));
// Produces: .. where `time` > NOW()
You can specify some of the expression properties through first argument of the constructor:
$expr = new Expression(["NOW()", 'connection' => $pdo]);
:ref:`Scroll down <properties>` for full list of properties.
When you create a template the first argument is the template. It will be stored in :php:attr:`$template` property. Template string can contain arguments in a square brackets:
coalesce([], [])is same ascoalesce([0], [1])coalesce([one], [two])
Arguments can be specified immediately through an array as a second argument into constructor or you can specify arguments later:
$expr = new Expression(
"coalesce([name], [surname])",
['name' => $name, 'surname' => $surname]
);
// is the same as
$expr = new Expression("coalesce([name], [surname])");
$expr['name'] = $name;
$expr['surname'] = $surname;
Expressions can be nested several times:
$age = new Expression("coalesce([age], [default_age])");
$age['age'] = new Expression("year(now()) - year(birth_date)");
$age['default_age'] = 18;
$query->table('user')->field($age, 'calculated_age');
// select coalesce(year(now()) - year(birth_date), :a) `calculated_age` from `user`
When you include one query into another query, it will automatically take care of all user-defined parameters (such as value 18 above) which will make sure that SQL injections could not be introduced at any stage.
An expression can be rendered into a valid SQL code by calling render() method. The method will return an array with string and params.
.. php:method:: render()
Converts :php:class:`Expression` object to an array with string and params.
Parameters are replaced with :a, :b, etc.
If your expression is a valid SQL query, (such as `show databases`) you
might want to execute it. Expression class offers you various ways to execute
your expression. Before you do, however, you need to have :php:attr:`$connection`
property set. (See Connecting to Database on more details). In short the
following code will connect your expression with the database:
$expr = new Expression('connection' => $pdo_dbh);
If you are looking to use connection :php:class:`Query` class, you may want to consider using a proper vendor-specific subclass:
$query = new \Atk4\Data\Persistence\Sql\Mysql\Query('connection' => $pdo_dbh);
If your expression already exist and you wish to associate it with connection you can simply change the value of :php:attr:`$connection` property:
$expr->connection = $pdo_dbh;
Finally, you can pass connection class into :php:meth:`execute` directly.
.. php:method:: execute($connection = null)
Executes expression using current database connection or the one you
specify as the argument::
$stmt = $expr->execute($pdo_dbh);
returns `Doctrine\DBAL\Result`.
.. todo::
Complete this when ResultSet and Connection are implemented
.. php:method:: expr($properties, $arguments)
Creates a new :php:class:`Expression` object that will inherit current
:php:attr:`$connection` property. Also if you are creating a
vendor-specific expression/query support, this method must return
instance of your own version of Expression class.
The main principle here is that the new object must be capable of working
with database connection.
.. php:method:: getRows()
Executes expression and return whole result-set in form of array of hashes::
$data = new Expression([
'connection' => $pdo_dbh,
'template' => 'show databases',
])->getRows();
echo json_encode($data);
The output would be
.. code-block:: json
[
{ "Database": "mydb1" },
{ "Database": "mysql" },
{ "Database": "test" },
]
.. php:method:: getRow()
Executes expression and returns first row of data from result-set as a hash::
$data = new Expression([
'connection' => $pdo_dbh,
'template' => 'SELECT @@global.time_zone, @@session.time_zone',
])->getRow()
echo json_encode($data);
The output would be
.. code-block:: json
{ "@@global.time_zone": "SYSTEM", "@@session.time_zone": "SYSTEM" }
.. php:method:: getOne()
Executes expression and return first value of first row of data from
result-set::
$time = new Expression([
'connection' => $pdo_dbh,
'template' => 'now()',
])->getOne();
.. php:method:: __toString()
You may use :php:class:`Expression` or :php:class:`Query` as a string. It
will be automatically executed when being cast by executing :php:meth:`getOne`.
Because the `__toString() <http://php.net/manual/en/language.oop5.magic.php#object.tostring>`_
is not allowed to throw exceptions we encourage you not to use this format.
.. php:method:: __debugInfo()
This method is used to prepare a sensible information about your query
when you are executing ``var_dump($expr)``. The output will be HTML-safe.
.. php:method:: debug()
Calling this method will set :php:attr:`debug` into ``true`` and the further
execution to :php:meth:`render` will also attempt to echo query.
.. php:method:: getDebugQuery()
Outputs query as a string by placing parameters into their respective
places. The parameters will be escaped, but you should still avoid using
generated query as it can potentially make you vulnerable to SQL injection.
This method will use HTML formatting if argument is passed.
In order for HTML parsing to work and to make your debug queries better formatted, install sql-formatter:
composer require jdorn/sql-formatter
The following methods are useful if you're building your own code for rendering parts of the query. You must not call them in normal circumstances.
.. php:method:: escape($value)
Creates new expression where $value appears escaped. Use this method as a
conventional means of specifying arguments when you think they might have
a nasty back-ticks or commas in the field names. I generally **discourage**
you from using this method. Example use would be::
$query->field('foo, bar'); // escapes and adds 2 fields to the query
$query->field($query->escape('foo, bar')); // adds field `foo, bar` to the query
$query->field(['foo, bar']); // adds single field `foo, bar`
$query->order('foo desc'); // escapes and add `foo` desc to the query
$query->field($query->escape('foo desc')); // adds field `foo desc` to the query
$query->field(['foo desc']); // adds `foo` desc anyway
.. php:method:: escapeIdentifier($sql_code)
Always surrounds `$sql code` with back-ticks.
This escaping method is automatically used for `{...}` expression template tags .
.. php:method:: escapeIdentifierSoft($sql_code)
Surrounds `$sql code` with back-ticks.
This escaping method is automatically used for `{{...}}` expression template tags .
It will smartly escape table.field type of strings resulting in `table`.`field`.
Will do nothing if it finds "*", "`" or "(" character in `$sql_code`::
$query->escapeIdentifierSoft('first_name'); // `first_name`
$query->escapeIdentifierSoft('first.name'); // `first`.`name`
$query->escapeIdentifierSoft('(2 + 2)'); // (2 + 2)
$query->escapeIdentifierSoft('*'); // *
.. php:method:: escapeParam($value)
Converts value into parameter and returns reference. Used only during query
rendering. Consider using :php:meth:`consume()` instead, which will also
handle nested expressions properly.
This escaping method is automatically used for `[...]` expression template tags .
.. php:attr:: template
Template which is used when rendering.
You can set this with either `new Expression("show tables")`
or `new Expression(["show tables"])`
or `new Expression(["template" => "show tables"])`.
.. php:attr:: connection
PDO connection object or any other DB connection object.
.. php:attr:: paramBase
Normally parameters are named :a, :b, :c. You can specify a different
param base such as :param_00 and it will be automatically increased
into :param_01 etc.
.. php:attr:: debug
If true, then next call of :php:meth:`execute` will ``echo`` results
of :php:meth:`getDebugQuery`.