Relation queries

The Serverpod query framework supports filtering on, sorting on, and including relational data structures. In SQL this is often achieved using a join operation. The functionality is available if there exists any one-to-one or one-to-many object relations between two models.

Include relational data

To include relational data in a query, use the include method. The include method has a typed interface and contains all the declared relations in your yaml file.

var employee = await Employee.db.findById(
  session,
  employeeId,
  include: Employee.include(
    address: Address.include(),
  ),
);

The example above return a employee including the related address object.

Nested includes

It is also possible to include deeply nested objects.

var employee = await Employee.db.findById(
  session,
  employeeId,
  include: Employee.include(
    company: Company.include(
      address: Address.include(),
    ),
  ),
);

The example above returns an employee including the related company object that has the related address object included.

Any relational object can be included or not when making a query but only the includes that are explicitly defined will be included in the result.

var user = await Employee.db.findById(
  session,
  employeeId,
  include: Employee.include(
    address: Address.include(),
    company: Company.include(
      address: Address.include(),
    ),
  ),
);

The example above includes several different objects configured by specifying the named parameters.

Include relational lists

Including a list of objects (1:n relation) can be done with the special includeList method. In the simplest case, the entire list is included.

var user = await Company.db.findById(
  session,
  employeeId,
  include: Company.include(
    employees: Employee.includeList(),
  ),
);

The example above returns a company with all related employees included.

Nested includes

The includeList method works slightly differently from a normal include and to include nested objects the includes field must be used. When including something on a list it means that every entry in the list will each have access to the nested object.

var user = await Company.db.findById(
  session,
  employeeId,
  include: Company.include(
    employees: Employee.includeList(
      includes: Employee.include(
        address: Address.include(),
      ),
    ),
  ),
);

The example above returns a company with all related employees included. Each employee will have the related address object included.

It is even possible to include lists within lists.

var user = await Company.db.findById(
  session,
  employeeId,
  include: Company.include(
    employees: Employee.includeList(
      includes: Employee.include(
        tools: Tool.includeList(),
      ),
    ),
  ),
);

The example above returns a company with all related employees included. Each employee will have the related tools list included.

note

For each call to includeList (nested or not) the Serverpod Framework will perform one additional query to the database.

Filter and sort

When working with large datasets, it's often necessary to filter and sort the records to retrieve the most relevant data. Serverpod offers methods to refine the included list of related objects:

Filter

Use the where clause to filter the results based on certain conditions.

var user = await Company.db.findById(
  session,
  employeeId,
  include: Company.include(
    employees: Employee.includeList(
      where: (t) => t.name.ilike('a%')
    ),
  ),
);`

The example above retrieves only employees whose names start with the letter 'a':

Sort

The orderBy clause lets you sort the results based on a specific field.

var user = await Company.db.findById(
  session,
  employeeId,
  include: Company.include(
    employees: Employee.includeList(
      orderBy: (t) => t.name,
    ),
  ),
);

The example above sorts the employees by their names in ascending order.

Pagination

Paginate results by specifying a limit on the number of records and an offset.

var user = await Company.db.findById(
  session,
  employeeId,
  include: Company.include(
    employees: Employee.includeList(
      limit: 10,
      offset: 10,
    ),
  ),
);

The example above retrieves the next 10 employees starting from the 11th record:

Using these methods in conjunction provides a powerful way to query, filter, and sort relational data efficiently.

Update

Managing relationships between tables is a common task. Serverpod provides methods to link (attach) and unlink (detach) related records:

Attach Single Row

Link an individual employee to a company. This operation associates an employee with a specific company:

var company = await Company.db.findById(session, companyId);
var employee = await Employee.db.findById(session, employeeId);

await Company.db.attachRow.employees(session, company!, employee!);

Bulk Attach Rows

For scenarios where you need to associate multiple employees with a company at once, use the bulk attach method. This operation is atomic, ensuring all or none of the records are linked:

var company = await Company.db.findById(session, companyId);
var employee = await Employee.db.findById(session, employeeId);

await Company.db.attach.employees(session, company!, [employee!]);

Detach Single Row

To remove the association between an employee and a company, use the detach row method:

var employee = await Employee.db.findById(session, employeeId);

await Company.db.detachRow.employees(session, employee!);

Bulk Detach Rows

In cases where you need to remove associations for multiple employees simultaneously, use the bulk detach method. This operation is atomic:

var employee = await Employee.db.findById(session, employeeId);

await Company.db.detach.employees(session, [employee!]);

note

When using the attach and detach methods the objects passed to them have to have the id field set.

The detach method is also required to have the related nested object set if you make the call from the side that does not hold the foreign key.