-
class
Expression
¶
Expressions¶
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 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`
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
Properties, Arguments, Parameters¶
Be careful when using those similar terms as they refer to different things:
- Properties refer to object properties, e.g. $expr->template, see Other Properties
- Arguments refer to template arguments, e.g. select * from [table], see Expression Template
- Parameters refer to the way of passing user values within a query where id=:a and are further explained below.
Parameters¶
Because some values are un-safe to use in the query and can contain dangerous values they are kept outside of the SQL query string and are using PDO’s bindParam instead. DSQL can consist of multiple objects and each object may have some parameters. During rendering those parameters are joined together to produce one complete query.
-
property
Expression::$
params
¶ This public property will contain the actual values of all the parameters. When multiple queries are merged together, their parameters are interlinked.
Creating Expression¶
use atk4\dsql\Expression;
$expr = new Expression("NOW()");
You can also use 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]);
Scroll down for full list of properties.
Expression Template¶
When you create a template the first argument is the template. It will be stored
in $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;
Nested expressions¶
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.
Rendering¶
An expression can be rendered into a valid SQL code by calling render() method. The method will return a string, however it will use references for parameters.
-
Expression::
render
()¶ Converts
Expression
object to a string. Parameters are replaced with :a, :b, etc. Their original values can be found inparams
.
Executing Expressions¶
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 $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 Query
class, you may want to
consider using a proper vendor-specific subclass:
$query = new Query_MySQL('connection'=>$pdo_dbh);
If your expression already exist and you wish to associate it with connection
you can simply change the value of $connection
property:
$expr -> connection = $pdo_dbh;
Finally, you can pass connection class into execute
directly.
-
Expression::
execute
($connection = null)¶ Executes expression using current database connection or the one you specify as the argument:
$stmt = $expr -> execute($pdo_dbh);
returns PDOStamement if you have used PDO class or ResultSet if you have used Connection.
-
Expression::
expr
($properties, $arguments)¶ Creates a new
Expression
object that will inherit current$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.
-
Expression::
get
()¶ Executes expression and return whole result-set in form of array of hashes:
$data = new Expression([ 'connection' => $pdo_dbh, 'template' => 'show databases' ])->get(); echo json_encode($data);
The output would be
[ { "Database": "mydb1" }, { "Database": "mysql" }, { "Database": "test" } ]
-
Expression::
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
{ "@@global.time_zone": "SYSTEM", "@@session.time_zone": "SYSTEM" }
-
Expression::
getOne
()¶ Executes expression and return first value of first row of data from result-set:
$time = new Expression([ 'connection' => $pdo_dbh, 'template' => 'now()' ])->getOne();
Magic an Debug Methods¶
-
Expression::
__toString
()¶ You may use
Expression
orQuery
as a string. It will be automatically executed when being cast by executinggetOne
. Because the __toString() is not allowed to throw exceptions we encourage you not to use this format.
-
Expression::
__debugInfo
()¶ This method is used to prepare a sensible information about your query when you are executing
var_dump($expr)
. The output will be HTML-safe.
-
Expression::
debug
()¶ Calling this method will set
debug
intotrue
and the further execution torender
will also attempt to echo query.
-
Expression::
getDebugQuery
($html = false)¶ Outputs query as a string by placing parameters into their respective places. The parameters will be escaped, but you should still avoid using generated query as it can potentially make you vulnerable to SQL injection.
This method will use HTML formatting if argument is passed.
In order for HTML parsing to work and to make your debug queries better formatted, install sql-formatter:
composer require jdorn/sql-formatter
Escaping Methods¶
The following methods are useful if you’re building your own code for rendering parts of the query. You must not call them in normal circumstances.
-
Expression::
_consume
($sql_code)¶ Makes $sql_code part of $this expression. Argument may be either a string (which will be escaped) or another
Expression
orQuery
. If specifiedQuery
is in “select” mode, then it’s automatically placed inside brackets:$query->_consume('first_name'); // `first_name` $query->_consume($other_query); // will merge parameters and return string
-
Expression::
escape
($sql_code)¶ Creates new expression where $sql_code 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 $query->field(['foo desc']); // adds `foo` desc anyway
-
Expression::
_escape
($sql_code)¶ Always surrounds $sql code with back-ticks.
-
Expression::
_escapeSoft
($sql_code)¶ Surrounds $sql code with back-ticks.
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->_escape('first_name'); // `first_name` $query->_escape('first.name'); // `first`.`name` $query->_escape('(2+2)'); // (2+2) $query->_escape('*'); // *
-
Expression::
_param
($value)¶ Converts value into parameter and returns reference. Used only during query rendering. Consider using
_consume()
instead, which will also handle nested expressions properly.
Other Properties¶
-
property
Expression::$
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”]).
-
property
Expression::$
connection
¶ PDO connection object or any other DB connection object.
-
property
Expression::$
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.
-
property
Expression::$
debug
¶ If true, then next call of
execute
willecho
results ofgetDebugQuery
.