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SQL queries

Most of the time you will be using the ORM abstraction layer to interact with the database (see Introduction to the Data Model and ORM), but sometimes you may need to do something very complex or specific which is hard to do with that abstraction.

Silverstripe CMS provides a lower level abstraction layer, which is used by the Silverstripe CMS ORM internally.

Dealing with low-level SQL is not encouraged, since the ORM provides powerful abstraction APIs. Records in collections are lazy loaded, and these collections have the ability to run efficient SQL such as counts or returning a single column.

For example, if you want to run a simple COUNT SQL statement, the following three statements are functionally equivalent:

use SilverStripe\ORM\DB;
use SilverStripe\ORM\Queries\SQLSelect;
use SilverStripe\Security\Member;

// Get the table for the "Member" class with ANSI quotes
$memberTable = DB::get_conn()->escapeIdentifier(
    DataObject::getSchema()->tableName(Member::class)
);

// Through raw SQL.
$count = DB::query('SELECT COUNT(*) FROM ' . $memberTable)->value();

// Through SQLSelect abstraction layer.
$count = SQLSelect::create('COUNT(*)', $memberTable)->execute()->value();

// Through the ORM.
$count = Member::get()->count();

If you do use raw SQL, you'll run the risk of breaking various assumptions the ORM and code based on it have:

Custom getter/setter methods (object property values can differ from database column values)
DataObject hooks like onBeforeWrite() and onBeforeDelete() if running low-level INSERT or UPDATE queries
Automatic casting
Default values set through objects
Database abstraction (some DataObject classes may not have their own tables, or may need a JOIN with other tables to get all of their field values)

We'll explain some ways to use the low-level APIs with the full power of SQL, but still maintain a connection to the ORM where possible.

Please read our security topic to find out how to properly prepare user input and variables for use in queries

Usage

Getting table names

Because of the way the ORM interacts with class inheritance, some models will spread their data across multiple tables. See Joining tables for a DataObject inheritance chain below for information about how to handle that scenario.

While you could hardcode table names into your SQL queries, that invites human error and means you have to make sure you know exactly what table stores which data for every class in the class hierarchy of the model you're interested in. Luckily, the DataObjectSchema class knows all about the database schema for your DataObject models. The following methods in particular may be useful to you:

baseDataTable(): Get the name of the database table which holds the base data (i.e. ID, ClassName, Created, etc) for a given DataObject class
classHasTable(): Check if there is a table in the database for a given DataObject class (i.e. whether that class defines columns not already present in another class further up the class hierarchy)
sqlColumnForField(): Get the ANSI-quoted table and column name for a given DataObject field (in "Table"."Field" format)
tableForField(): Get the table name in the class hierarchy which contains a given field column.
tableName(): Get table name for the given class. Note that this does not confirm a table actually exists (or should exist), but returns the name that would be used if this table did exist. Make sure to call classHasTable() before using this table name in a query.

While the default database connector will work fine without explicitly ANSI-quoting table names in queries, it is good practice to make sure they are quoted (especially if you're writing these queries in a module that will be publicly shared) to ensure your queries will work on other database connectors such as PostgreSQLDatabase which explicitly require ANSI quoted table names.

You can do that by passing the raw table name into DB::get_conn()->escapeIdentifier(), which will ensure it is correctly escaped according to the rules of the currently active database connector.

SELECT

Selection can be done by creating an instance of SQLSelect, which allows management of all elements of a SQL SELECT query, including columns, joined tables, conditional filters, grouping, limiting, and sorting.

For example:

$schema = DataObject::getSchema();
$playerTableName = DB::get_conn()->escapeIdentifier($schema->baseDataTable(Player::class));

$sqlQuery = new SQLSelect();
$sqlQuery->setFrom($playerTableName);

// Add a column to the `SELECT ()` clause
$sqlQuery->selectField('FieldName');
// You can pass an alias for the field in as the second argument
$sqlQuery->selectField('YEAR("Birthday")', 'Birthyear');

// Join another table onto the query
$teamIdField = $schema->sqlColumnForField(Player::class, 'TeamID');
$idField = $schema->sqlColumnForField(Team::class, 'ID');
$joinOnClause = "$teamIdField = $idField";
$sqlQuery->addLeftJoin($teamTableName, $joinOnClause);

// Combine another query using a union
$sqlQuery->addUnion($anotherSqlSelect, SQLSelect::UNION_ALL);

// There are methods for most SQL clauses, such as WHERE, ORDER BY, GROUP BY, etc
$sqlQuery->addWhere(['YEAR("Birthday") = ?' => 1982]);
// $sqlQuery->setOrderBy(...);
// $sqlQuery->setGroupBy(...);
// $sqlQuery->setHaving(...);
// $sqlQuery->setLimit(...);
// $sqlQuery->setDistinct(true);

// Get the raw SQL (optional) and parameters
$rawSQL = $sqlQuery->sql($parameters);

// Execute and return a Query object
$result = $sqlQuery->execute();

// Iterate over results
foreach ($result as $row) {
    echo $row['BirthYear'];
}

There's a lot to this API - we highly recommend that you check out the PHPDoc comments on the methods in this class to learn more about the specific usages of each - for example, the addWhere() method's PHPDoc includes multiple examples of different syntaxes that can be passed into it.

The result of SQLSelect::execute() is an array lightly wrapped in a database-specific subclass of Query. This class implements the IteratorAggregate interface, and provides convenience methods for accessing the data.

DELETE

Deletion can be done either by creating a SQLDelete object, or by transforming a SQLSelect into a SQLDelete object instead.

For example, creating a SQLDelete object:

use SilverStripe\CMS\Model\SiteTree;
use SilverStripe\ORM\DB;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLDelete;

$schema = DataObject::getSchema();
$siteTreeTable = DB::get_conn()->escapeIdentifier($schema->baseDataTable(SiteTree::class));

$query = SQLDelete::create()
    ->setFrom($siteTreeTable)
    ->setWhere([$schema->sqlColumnForField(SiteTree::class, 'ShowInMenus') => 0]);
$query->execute();

Alternatively, turning an existing SQLSelect into a delete:

use SilverStripe\CMS\Model\SiteTree;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLSelect;

$schema = DataObject::getSchema();
$siteTreeTable = DB::get_conn()->escapeIdentifier($schema->baseDataTable(SiteTree::class));

$query = SQLSelect::create()
    ->setFrom($siteTreeTable)
    ->setWhere([$schema->sqlColumnForField(SiteTree::class, 'ShowInMenus') => 0])
    ->toDelete();
$query->execute();

INSERT/UPDATE

INSERT and UPDATE can be performed using the SQLInsert and SQLUpdate classes. These both have similar aspects in that they can modify content in the database, but each are different in the way in which they behave.

These operations can be performed in batches by using the DB::manipulate method, which internally uses SQLUpdate / SQLInsert.

Each of these classes implement the SQLWriteExpression interface, noting that each accepts key/value pairs in a number of similar ways. These include the following API methods:

addAssignments() - Takes a list of assignments as an associative array of key => value pairs, where the value can also be an SQL expression.
setAssignments() - Replaces all existing assignments with the specified list
getAssignments() - Returns all currently given assignments, as an associative array in the format ['Column' => ['SQL' => ['parameters]]]
assign() - Singular form of addAssignments(), but only assigns a single column value
assignSQL() - Assigns a column the value of a specified SQL expression without parameters - assignSQL('Column', 'SQL') is shorthand for assign('Column', ['SQL' => []])

SQLUpdate also includes the following API methods:

clear() - Clears all assignments
getTable() - Gets the table to update
setTable() - Sets the table to update (this should be ANSI-quoted) e.g. $query->setTable('"Page"');

SQLInsert also includes the following API methods:

clear() - Clears all rows
clearRow() - Clears all assignments on the current row
addRow() - Adds another row of assignments, and sets the current row to the new row
addRows() - Adds a number of arrays, each representing a list of assignment rows, and sets the current row to the last one
getColumns() - Gets the names of all distinct columns assigned
getInto() - Gets the table to insert into
setInto() - Sets the table to insert into (this should be ANSI-quoted), e.g. $query->setInto('"Page"');

For example:

use SilverStripe\CMS\Model\SiteTree;
use SilverStripe\ORM\DB;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLUpdate;

$schema = DataObject::getSchema();
$siteTreeTable = DB::get_conn()->escapeIdentifier($schema->baseDataTable(SiteTree::class));

$update = SQLUpdate::create($siteTreeTable)->addWhere(['"ID"' => 3]);

// assigning a list of items
$update->addAssignments([
    '"Title"' => 'Our Products',
    '"MenuTitle"' => 'Products',
]);

// Assigning a single value
$update->assign('"MenuTitle"', 'Products');

// Assigning a value using parameterised expression
$title = 'Products';
$update->assign('"MenuTitle"', [
    'CASE WHEN LENGTH("MenuTitle") > LENGTH(?) THEN "MenuTitle" ELSE ? END' =>
        [$title, $title],
]);

// Assigning a value using a pure SQL expression
$update->assignSQL('"Date"', 'NOW()');

// Perform the update
$update->execute();

In addition to assigning values, the SQLInsert object also supports multi-row inserts. For database connectors and API that don't have multi-row insert support these are translated internally as multiple single row inserts.

For example:

use SilverStripe\CMS\Model\SiteTree;
use SilverStripe\ORM\DB;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLInsert;

$schema = DataObject::getSchema();
$siteTreeTable = DB::get_conn()->escapeIdentifier($schema->baseDataTable(SiteTree::class));

$insert = SQLInsert::create($siteTreeTable);

// Add multiple rows in a single call. Note that column names do not need to be symmetric
$insert->addRows([
    ['"Title"' => 'Home', '"Content"' => '<p>This is our home page</p>'],
    ['"Title"' => 'About Us', '"ClassName"' => 'AboutPage'],
]);

// Adjust an assignment on the last row
$insert->assign('"Content"', '<p>This is about us</p>');

// Add another row
$insert->addRow(['"Title"' => 'Contact Us']);

// $columns will be ['"Title"', '"Content"', '"ClassName"'];
$columns = $insert->getColumns();

$insert->execute();

Value checks

Raw SQL is handy for performance-optimized calls, e.g. when you want a single column rather than a full-blown object representation.

Example: Get the count from a relationship.

use SilverStripe\ORM\DB;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLSelect;

$schema = DataObject::getSchema();
$playerTableName = DB::get_conn()->escapeIdentifier($schema->baseDataTable(Player::class));
$teamTableName = DB::get_conn()->escapeIdentifier($schema->baseDataTable(Team::class));
$playerIdField = $schema->sqlColumnForField(Player::class, 'ID');
$playerTeamIdField = $schema->sqlColumnForField(Player::class, 'TeamID');
$teamIdField = $schema->sqlColumnForField(Team::class, 'ID');

$sqlQuery = new SQLSelect();
$sqlQuery->setFrom($playerTableName);
$sqlQuery->addSelect('COUNT(' . $playerIdField . ')');
$sqlQuery->addWhere([$teamIdField => 99]);
$sqlQuery->addLeftJoin('Team', $teamIdField ' = ' . $playerTeamIdField);
$count = $sqlQuery->execute()->value();

Note that in the ORM, this call would be executed in an efficient manner as well:

$count = $myTeam->Players()->count();

Value placeholders

In some of the examples here you will have noticed a ? as part of the query, which is a placeholder for a value. This is called a "parameterized" or "prepared" query and is a good way to make sure your values are correctly escaped automatically to help protect yourself against SQL injection attacks.

With some queries you'll know ahead of time how many values you're including in your query, but sometimes (most notably when using the IN SQL operator) you will have a lot of values or a variable number of values and it can be difficult to get the correct number of ? placeholders.

In those cases, you can use the DB::placeholders() method, which prepares these placeholders for you.

If you need this for some thing other than inclusion in an IN SQL operation, you can pass a custom delimiter as the second argument to DB::placeholders().

Also note that you can pass an integer in as the first argument rather than an array of values, if you want.

Example: Get the fields for all players in a team which has more than 15 wins.

use SilverStripe\ORM\DB;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLSelect;

$schema = DataObject::getSchema();
$playerTableName = DB::get_conn()->escapeIdentifier($schema->baseDataTable(Player::class));

$teamIds = Team::get()->filter('Wins:GreaterThan', 15)->column('ID');
$placeholders = DB::placeholders($teamIds);

$sqlQuery = new SQLSelect();
$sqlQuery->setFrom($playerTableName)->where([
    $schema->sqlColumnForField(Player::class, 'ID') . ' in (' . $placeholders . ')' => $ids,
]);
$results = $sqlQuery->execute();

This is obviously a contrived example - this could easily (and more efficiently) be done using the ORM:

$players = Player::get()->filter('Teams.Wins:GreaterThan', 15);

Joining tables for a `DataObject` inheritance chain

In the Introduction to the Data Model and ORM we discussed how DataObject inheretance chains can spread their data across multiple tables. The ORM handles this seemlessly, but when using the lower-level APIs we need to account for this ourselves by joining all of the relevant tables manually.

We also want to make sure to only select the records which are relevant for the actual class in the class hierarchy we're looking at. To do that, we can either use an INNER JOIN, or we can use a WHERE clause on the ClassName field. In the below example we're using a WHERE clause with a LEFT JOIN because it is likely more intuitive for developers who aren't intimately familar with SQL.

use SilverStripe\ORM\DB;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLSelect;

$schema = DataObject::getSchema();
$computerBaseTable = DB::get_conn()->escapeIdentifier($schema->baseDataTable(Computer::class));

$select = new SQLSelect();
$select->setFrom($computerTable);
$select->addWhere([$schema->sqlColumnForField(Computer::class, 'ClassName') => Computer::class]);

// Get all fields included in the query
$columns = $select->getSelect();
// If we're doing a "SELECT *" (which is the default select), get the field names from the DataObjectSchema instead
if (count($columns) === 1 && array_key_first($columns) === '*') {
    $columns = $schema->fieldSpecs(Computer::class);
}

// Make sure we join all the tables in the inheritance chain which are required for this query
foreach ($columns as $alias => $ansiQuotedColumn) {
    if ($schema->fieldSpec(Computer::class, $alias, DataObjectSchema::DB_ONLY)) {
        $fieldTable = $schema->tableForField(Computer::class, $alias);
        if (!$select->isJoinedTo($fieldTable)) {
            $quotedFieldTable = DB::get_conn()->escapeIdentifier($fieldTable);
            $joinOnClause = $schema->sqlColumnForField(Computer::class, 'ID') . ' = ' . $quotedFieldTable . '."ID"';
            $select->addLeftJoin($quotedFieldTable, $joinOnClause);
        }
    }
}

If we want all of the fields for all models in the class hierarchy (mimicking Product::get() where Product is the first subclass of DataObject - see the example in the Introduction to the Data Model and ORM), we can do this by using a LEFT JOIN (like above), ommitting the WHERE clause on the ClassName field, and making sure we join all tables for the inheritance chain regardless of the fields being selected. To do that, make sure you're using the first DataObject class as your first main query class (replace Computer above with Product, in this example), remove the call to $select->addWhere(), and add the following code to the end of the above example:

// Make sure we join all the tables for the model inheritance chain
foreach (ClassInfo::subclassesFor(Product::class, includeBaseClass: false) as $class) {
    if ($schema->classHasTable($class)) {
        $classTable = $schema->tableName($class);
        if (!$select->isJoinedTo($classTable)) {
            $quotedClassTable = DB::get_conn()->escapeIdentifier($classTable);
            $joinOnClause = $schema->sqlColumnForField(Product::class, 'ID') . ' = ' . $quotedClassTable . '."ID"';
            $select->addLeftJoin($quotedClassTable, $joinOnClause);
        }
    }
}

Common table expressions (CTE aka the `WITH` clause)

Common Table Expressions are a powerful tool both for optimising complex queries, and for creating recursive queries. You can use these by calling the SQLSelect::addWith() method.

Older database servers don't support this functionality, and the core implementation is only valid for MySQL (though community modules may add support for other database connectors). If you are using this functionality in an open source module or a project that you can't guarantee the type and version of database being used, you should wrap the query in a condition checking if CTEs are supported. You can do that by calling DB::get_conn()->supportsCteQueries().

if (DB::get_conn()->supportsCteQueries(true)) {
    // Supports recursive CTE clause
} elseif (DB::get_conn()->supportsCteQueries()) {
    // Supports non-recursive CTE clause
} else {
    // No CTE support
}

For an example of how to use this abstraction and how powerful it is, here is an example query that recursively fetches the ancestors of a given record.

use App\Model\ObjectWithParent;
use SilverStripe\Core\Convert;
use SilverStripe\ORM\DB;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLSelect;

$schema = DataObject::getSchema();
$tableName = Convert::symbol2sql($schema->baseDataTable(ObjectWithParent::class));
$parentIdField = $schema->sqlColumnForField(ObjectWithParent::class, 'ParentID');
$idField = $schema->sqlColumnForField(ObjectWithParent::class, 'ID');
$cteIdField = Convert::symbol2sql('hierarchy_cte.parent_id');

// Only use the CTE functionality if it is supported by the current database
if (DB::get_conn()->supportsCteQueries(true)) {
    $baseQuery = SQLSelect::create()->setFrom($tableName);
    $cteQuery = SQLSelect::create(
        $parentIdField,
        $tableName,
        [
            "$parentIdField > 0",
            $idField => $someRecord->ID,
        ]
    );
    $recursiveQuery = SQLSelect::create(
        $parentIdField,
        ['"hierarchy_cte"', $tableName],
        [
            "$parentIdField > 0",
            "$idField = $cteIdField",
        ]
    );
    $cteQuery->addUnion($recursiveQuery);
    $baseQuery->addWith('hierarchy_cte', $cteQuery, ['parent_id'], true)
        ->addInnerJoin('hierarchy_cte', "$idField = $cteIdField");
    // This query result will include only the ancestors of whatever record is stored in the $someRecord variable.
    $ancestors = $baseQuery->execute();
} else {
    // provide an alternative implementation, e.g. a recursive PHP method which runs a query at each iteration
}

The SQL for that query, in MySQL, would look something like this:

WITH RECURSIVE "hierarchy_cte" ("parent_id") AS (
    (
        SELECT "ObjectWithParent"."ParentID" FROM "ObjectWithParent"
        WHERE ("ObjectWithParent"."ParentID" > 0) AND ("ObjectWithParent"."ID" = ?)
    ) UNION (
        SELECT "ObjectWithParent"."ParentID" FROM "hierarchy_cte", "ObjectWithParent"
        WHERE ("ObjectWithParent"."ParentID" > 0) AND ("ObjectWithParent"."ID" = "hierarchy_cte"."parent_id")
    )
)
SELECT * FROM "ObjectWithParent" INNER JOIN "hierarchy_cte" ON "ObjectWithParent"."ID" = "hierarchy_cte"."parent_id"

The PHPDoc for the SQLSelect::addWith() method has more details about what each of the arguments are and how they're used, though note that you should ensure you understand the underlying SQL concept of CTE queries before using this API.

Mapping

Creates a map based on the first two columns of the query result. This can be useful for creating dropdowns.

Example: Show player names with their birth year, but set their birth dates as values.

use SilverStripe\Forms\DropdownField;
use SilverStripe\ORM\DB;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLSelect;

$schema = DataObject::getSchema();
$playerTableName = DB::get_conn()->escapeIdentifier($schema->baseDataTable(Player::class));

$sqlQuery = new SQLSelect();
$sqlQuery->setFrom($playerTableName);
$sqlQuery->setSelect('"ID"');
$sqlQuery->selectField('CONCAT("Name", \' - \', YEAR("Birthdate")', 'NameWithBirthyear');
$map = $sqlQuery->execute()->map();

// The value of the selected option will be the record ID, and the display label will be the name and
// birthyear concatenation.
$field = new DropdownField('Birthdates', 'Birthdates', $map);

Note that going through SQLSelect is only necessary here because of the custom SQL value transformation (YEAR()). An alternative approach would be a custom getter in the object definition:

namespace App\Model;

use SilverStripe\ORM\DataObject;

class Player extends DataObject
{
    private static $db = [
        'Name' => 'Varchar',
        'Birthdate' => 'Date',
    ];

    public function getNameWithBirthyear()
    {
        return date('y', $this->Birthdate);
    }
}

use App\Model\Player;

$players = Player::get();
$map = $players->map('ID', 'NameWithBirthyear');

True raw SQL

Up until now we've still been using an abstraction layer to perform SQL queries - but there might be times where it's just cleaner to explicitly use raw SQL. You can do that with either the DB::query() or DB::prepared_query() method.

Directly querying the database:

use SilverStripe\CMS\Model\SiteTree;
use SilverStripe\ORM\DB;
use SilverStripe\ORM\DataObject;

$schema = DataObject::getSchema();
$siteTreeBaseTable = DB::get_conn()->escapeIdentifier($schema->baseDataTable(SiteTree::class));
$showInMenusField = $schema->sqlColumnForField(SiteTree::class, 'ShowInMenus');

// Use DB::query() if you don't need to pass in any parameters (values)
$count = DB::query('SELECT COUNT(*) FROM ' . $siteTreeBaseTable)->value();

// Use DB::prepared_query() if you need to pass in some parameters (values) e.g. for WHERE clauses
$results = DB::prepared_query('DELETE FROM ' . $siteTreeBaseTable . ' WHERE ' . $showInMenusField . ' = ?', [0]);
foreach ($results as $row) {
    // $row is an array representing the database row, just like with SQLSelect.
}

Note that you do not have to call execute() with these methods, unlike the abstraction layer in the other examples. This is because you're passing the entire query into the method - you can't change the query after it's passed in, so it gets executed right away. The return type for these methods is the same as the return type for the execute() methods on the SQLExpression classes.

Data types

The following PHP types are used to return database content:

booleans will be an integer 1 or 0, to ensure consistency with MySQL that doesn't have native booleans
integer types returned as integers
floating point / decimal types returned as floats
strings returned as strings
dates / datetimes returned as strings

API documentation

Edit on Github

SQL queries#

Usage#

Getting table names#

SELECT#

DELETE#

INSERT/UPDATE#

Value checks#

Value placeholders#

Joining tables for a DataObject inheritance chain#

Common table expressions (CTE aka the WITH clause)#

Mapping#

True raw SQL#

Data types#

Related documentation#

API documentation#

SQL queries

Usage

Getting table names

SELECT

DELETE

INSERT/UPDATE

Value checks

Value placeholders

Joining tables for a `DataObject` inheritance chain

Common table expressions (CTE aka the `WITH` clause)

Mapping

True raw SQL

Data types

Related documentation

API documentation