Data Retrieval And Manipulation

Dynamic Parameters and Prepared Statements

Consider the previous query, now parameterized to fetch only a single article by id. Using ext/mysql (still the primary choice of MySQL access for many developers) you had to escape every value passed into the query using mysql_real_escape_string() to avoid SQL injection:

1
<?php
$sql = "SELECT * FROM articles WHERE id = '" . mysql_real_escape_string($id, $link) . "'";
$rs = mysql_query($sql);
2
3

If you start adding more and more parameters to a query (for example in UPDATE or INSERT statements) this approach might lead to complex to maintain SQL queries. The reason is simple, the actual SQL query is not clearly separated from the input parameters. Prepared statements separate these two concepts by requiring the developer to add placeholders to the SQL query (prepare) which are then replaced by their actual values in a second step (execute).

1
<?php
// $conn instanceof Doctrine\DBAL\Connection

$sql = "SELECT * FROM articles WHERE id = ?";
$stmt = $conn->prepare($sql);
$stmt->bindValue(1, $id);
$resultSet = $stmt->executeQuery();
2
3
4
5
6
7

Placeholders in prepared statements are either simple positional question marks (?) or named labels starting with a colon (e.g. :name1). You cannot mix the positional and the named approach. You have to bind a parameter to each placeholder.

The approach using question marks is called positional, because the values are bound in order from left to right to any question mark found in the previously prepared SQL query. That is why you specify the position of the variable to bind into the bindValue() method:

1
<?php
// $conn instanceof Doctrine\DBAL\Connection

$sql = "SELECT * FROM articles WHERE id = ? AND status = ?";
$stmt = $conn->prepare($sql);
$stmt->bindValue(1, $id);
$stmt->bindValue(2, $status);
$resultSet = $stmt->executeQuery();
2
3
4
5
6
7
8

Named parameters have the advantage that their labels can be re-used and only need to be bound once:

1
<?php
// $conn instanceof Doctrine\DBAL\Connection

$sql = "SELECT * FROM users WHERE name = :name OR username = :name";
$stmt = $conn->prepare($sql);
$stmt->bindValue("name", $name);
$resultSet = $stmt->executeQuery();
2
3
4
5
6
7

The following section describes the API of Doctrine DBAL with regard to prepared statements.

Using Prepared Statements

There are three low-level methods on Doctrine\DBAL\Connection that allow you to use prepared statements:

• prepare($sql) - Create a prepared statement of the type Doctrine\DBAL\Statement. Using this method is preferred if you want to re-use the statement to execute several queries with the same SQL statement only with different parameters.
• executeQuery($sql, $params, $types) - Create a prepared statement for the passed SQL query, bind the given params with their binding types and execute the query. This method returns the executed prepared statement for iteration and is useful for SELECT statements.
• executeStatement($sql, $params, $types) - Create a prepared statement for the passed SQL query, bind the given params with their binding types and execute the query. This method returns the number of affected rows by the executed query and is useful for UPDATE, DELETE and INSERT statements.

A simple usage of prepare was shown in the previous section, however it is useful to dig into the features of a Doctrine\DBAL\Statement a little bit more. There are essentially two different types of methods available on a statement. Methods for binding parameters and types and methods to retrieve data from a statement.

• bindValue($pos, $value, $type) - Bind a given value to the positional or named parameter in the prepared statement.
• bindParam($pos, &$param, $type) - Bind a given reference to the positional or named parameter in the prepared statement.

If you are finished with binding parameters you have to call executeQuery() on the statement, which will trigger a query to the database. After the query is finished, a Doctrine\DBAL\Result instance is returned and you can access the results of this query using the fetch API of the result:

• fetchNumeric() - Retrieves the next row from the statement or false if there are none. The row is fetched as an array with numeric keys where the columns appear in the same order as they were specified in the executed SELECT query. Moves the pointer forward one row, so that consecutive calls will always return the next row.
• fetchAssociative() - Retrieves the next row from the statement or false if there are none. The row is fetched as an associative array where the keys represent the column names as specified in the executed SELECT query. Moves the pointer forward one row, so that consecutive calls will always return the next row.
• fetchOne() - Retrieves the value of the first column of the next row from the statement or false if there are none. Moves the pointer forward one row, so that consecutive calls will always return the next row.
• fetchAllNumeric() - Retrieves all rows from the statement as arrays with numeric keys.
• fetchAllAssociative() - Retrieves all rows from the statement as associative arrays.
• fetchFirstColumn() - Retrieves the value of the first column of all rows.

The fetch API of a prepared statement obviously works only for SELECT queries. If you want to execute a statement that does not yield a result set, like INSERT, UPDATE or DELETE for instance, you might want to call executeStatement() instead of executeQuery().

If you find it tedious to write all the prepared statement code you can alternatively use the Doctrine\DBAL\Connection#executeQuery() and Doctrine\DBAL\Connection#executeStatement() methods. See the API section below on details how to use them.

Additionally there are lots of convenience methods for data-retrieval and manipulation on the Connection, which are all described in the API section below.

DoctrineDBALTypes Conversion

If you don't specify an integer (through one of Doctrine\DBAL\ParameterType constants) to any of the parameter binding methods but a string, Doctrine DBAL will ask the type abstraction layer to convert the passed value from its PHP to a database representation. This way you can pass \DateTime instances to a prepared statement and have Doctrine convert them to the appropriate vendors database format:

1
<?php
$date = new \DateTime("2011-03-05 14:00:21");
$stmt = $conn->prepare("SELECT * FROM articles WHERE publish_date > ?");
$stmt->bindValue(1, $date, "datetime");
$resultSet = $stmt->executeQuery();
2
3
4
5

If you take a look at Doctrine\DBAL\Types\DateTimeType you will see that parts of the conversion are delegated to a method on the current database platform, which means this code works independent of the database you are using.

List of Parameters Conversion

One rather annoying bit of missing functionality in SQL is the support for lists of parameters. You cannot bind an array of values into a single prepared statement parameter. Consider the following very common SQL statement:

1
SELECT * FROM articles WHERE id IN (?)

Since you are using an IN expression you would really like to use it in the following way (and I guess everybody has tried to do this once in their life, before realizing it doesn't work):

1
<?php
$stmt = $conn->prepare('SELECT * FROM articles WHERE id IN (?)');
// THIS WILL NOT WORK:
$stmt->bindValue(1, [1, 2, 3, 4, 5, 6]);
$resultSet = $stmt->executeQuery();
2
3
4
5

Implementing a generic way to handle this kind of query is tedious work. This is why most developers fallback to inserting the parameters directly into the query, which can open SQL injection possibilities if not handled carefully.

Doctrine DBAL implements a very powerful parsing process that will make this kind of prepared statement possible natively in the binding type system. The parsing necessarily comes with a performance overhead, but only if you really use a list of parameters. There are four special binding types that describe a list of integers, regular, ascii or binary strings:

• \Doctrine\DBAL\ArrayParameterType::INTEGER
• \Doctrine\DBAL\ArrayParameterType::STRING
• \Doctrine\DBAL\ArrayParameterType::ASCII
• \Doctrine\DBAL\ArrayParameterType::BINARY

Using one of these constants as a type you can activate the SQLParser inside Doctrine that rewrites the SQL and flattens the specified values into the set of parameters. Consider our previous example:

1
<?php
$stmt = $conn->executeQuery('SELECT * FROM articles WHERE id IN (?)',
    [[1, 2, 3, 4, 5, 6]],
    [\Doctrine\DBAL\ArrayParameterType::INTEGER]
);
2
3
4
5

The SQL statement passed to Connection#executeQuery is not the one actually passed to the database. It is internally rewritten to look like the following explicit code that could be specified as well:

1
<?php
// Same SQL WITHOUT usage of Doctrine\DBAL\ArrayParameterType::INTEGER
$stmt = $conn->executeQuery('SELECT * FROM articles WHERE id IN (?, ?, ?, ?, ?, ?)',
    [1, 2, 3, 4, 5, 6],
    [
        ParameterType::INTEGER,
        ParameterType::INTEGER,
        ParameterType::INTEGER,
        ParameterType::INTEGER,
        ParameterType::INTEGER,
        ParameterType::INTEGER,
    ]
);
2
3
4
5
6
7
8
9
10
11
12
13

This is much more complicated and is ugly to write generically.

prepare()

Prepare a given SQL statement and return the \Doctrine\DBAL\Statement instance:

1
<?php
$statement = $conn->prepare('SELECT * FROM user');
$resultSet = $statement->executeQuery();
$users = $resultSet->fetchAllAssociative();

/*
array(
  0 => array(
    'username' => 'jwage',
    'email' => 'j.wage@example.com'
  )
)
*/
2
3
4
5
6
7
8
9
10
11
12
13

executeStatement()

Executes a prepared statement with the given SQL and parameters and returns the affected rows count:

1
<?php
$count = $conn->executeStatement('UPDATE user SET username = ? WHERE id = ?', ['jwage', 1]);
echo $count; // 1
2
3

The $types variable contains the PDO or Doctrine Type constants to perform necessary type conversions between actual input parameters and expected database values. See the Types section for more information.

executeQuery()

Creates a prepared statement for the given SQL and passes the parameters to the executeQuery method, then returning the result set:

1
<?php
$resultSet = $conn->executeQuery('SELECT * FROM user WHERE username = ?', ['jwage']);
$user = $resultSet->fetchAssociative();

/*
array(
  0 => 'jwage',
  1 => 'j.wage@example.com'
)
*/
2
3
4
5
6
7
8
9
10

The $types variable contains the PDO or Doctrine Type constants to perform necessary type conversions between actual input parameters and expected database values. See the Types section for more information.

fetchAllAssociative()

Execute the query and fetch all results into an array:

1
<?php
$users = $conn->fetchAllAssociative('SELECT * FROM user');

/*
array(
  0 => array(
    'username' => 'jwage',
    'email' => 'j.wage@example.com'
  )
)
*/
2
3
4
5
6
7
8
9
10
11

fetchAllKeyValue()

Execute the query and fetch the first two columns into an associative array as keys and values respectively:

1
<?php
$users = $conn->fetchAllKeyValue('SELECT username, email FROM user');

/*
array(
  'jwage' => 'j.wage@example.com',
)
*/
2
3
4
5
6
7
8

fetchAllAssociativeIndexed()

Execute the query and fetch the data as an associative array where the key represents the first column and the value is an associative array of the rest of the columns and their values:

1
<?php
$users = $conn->fetchAllAssociativeIndexed('SELECT id, username, email FROM user');

/*
array(
    1 => array(
      'username' => 'jwage',
      'email' => 'j.wage@example.com'
    )
)
*/
2
3
4
5
6
7
8
9
10
11

fetchNumeric()

Numeric index retrieval of first result row of the given query:

1
<?php
$user = $conn->fetchNumeric('SELECT * FROM user WHERE username = ?', ['jwage']);

/*
array(
  0 => 'jwage',
  1 => 'j.wage@example.com'
)
*/
2
3
4
5
6
7
8
9

fetchOne()

Retrieve only the value of the first column of the first result row.

1
<?php
$username = $conn->fetchOne('SELECT username FROM user WHERE id = ?', [1], 0);
echo $username; // jwage
2
3

fetchAssociative()

Retrieve associative array of the first result row.

1
<?php
$user = $conn->fetchAssociative('SELECT * FROM user WHERE username = ?', ['jwage']);
/*
array(
  'username' => 'jwage',
  'email' => 'j.wage@example.com'
)
*/
2
3
4
5
6
7
8

There are also convenience methods for data manipulation queries:

iterateKeyValue()

Execute the query and iterate over the first two columns as keys and values respectively:

1
<?php
foreach ($conn->iterateKeyValue('SELECT username, email FROM user') as $username => $email) {
    // ...
}
2
3
4

iterateAssociativeIndexed()

Execute the query and iterate over the result with the key representing the first column and the value being an associative array of the rest of the columns and their values:

1
<?php
foreach ($conn->iterateAssociativeIndexed('SELECT id, username, email FROM user') as $id => $data) {
    // ...
}
2
3
4

delete()

Delete all rows of a table matching the given identifier, where keys are column names.

1
<?php
$conn->delete('user', ['id' => 1]);
// DELETE FROM user WHERE id = ? (1)
2
3

insert()

Insert a row into the given table name using the key value pairs of data.

1
<?php
$conn->insert('user', ['username' => 'jwage']);
// INSERT INTO user (username) VALUES (?) (jwage)
2
3

update()

Update all rows for the matching key value identifiers with the given data.

1
<?php
$conn->update('user', ['username' => 'jwage'], ['id' => 1]);
// UPDATE user SET username = ? WHERE id = ? (jwage, 1)
2
3