drift/docs/pages/docs/Using SQL/custom_queries.md

data	aliases	template
title weight description Custom queries 10 Let drift generate Dart from your SQL statements	/queries/custom	layouts/docs/single

Although drift includes a fluent api that can be used to model most statements, advanced features like WITH clauses or subqueries aren't supported yet. You can use these features with custom statements. You don't have to miss out on other benefits drift brings, though: Drift helps you parse the result rows and custom queries also support auto-updating streams.

Statements with a generated api

You can instruct drift to automatically generate a typesafe API for your select, update and delete statements. Of course, you can still write custom sql manually. See the sections below for details.

To use this feature, all you need to is define your queries in your DriftDatabase annotation:

@DriftDatabase(
  tables: [Todos, Categories],
  queries: {
    'categoriesWithCount':
        'SELECT *, (SELECT COUNT(*) FROM todos WHERE category = c.id) AS "amount" FROM categories c;'
  },
)
class MyDatabase extends _$MyDatabase {
  // rest of class stays the same
}

After running the build step again, drift will have written the CategoriesWithCountResult class for you - it will hold the result of your query. Also, the _$MyDatabase class from which you inherit will have the methods categoriesWithCount (which runs the query once) and watchCategoriesWithCount (which returns an auto-updating stream).

Queries can have parameters in them by using the ? or :name syntax. When your queries contains parameters, drift will figure out an appropriate type for them and include them in the generated methods. For instance, 'categoryById': 'SELECT * FROM categories WHERE id = :id' will generate the method categoryById(int id).

{% block "blocks/alert" title="On table names" color="info" %} To use this feature, it's helpful to know how Dart tables are named in sql. For tables that don't override tableName, the name in sql will be the snake_case of the class name. So a Dart table called Categories will be named categories, a table called UserAddressInformation would be called user_address_information. The same rule applies to column getters without an explicit name. Tables and columns declared in [Drift files]({{ "drift_files.md" | pageUrl }}) will always have the name you specified. {% endblock %}

You can also use UPDATE or DELETE statements here. Of course, this feature is also available for [daos]({{ "../Advanced Features/daos.md" | pageUrl }}), and it perfectly integrates with auto-updating streams by analyzing what tables you're reading from or writing to.

Custom select statements

If you don't want to use the statements with an generated api, you can still send custom queries by calling customSelect for a one-time query or customSelectStream for a query stream that automatically emits a new set of items when the underlying data changes. Using the todo example introduced in the [getting started guide]({{ "../Getting started/index.md" | pageUrl }}), we can write this query which will load the amount of todo entries in each category:

class CategoryWithCount {
  final Category category;
  final int count; // amount of entries in this category

  CategoryWithCount(this.category, this.count);
}

// then, in the database class:
Stream<List<CategoryWithCount>> categoriesWithCount() {
    // select all categories and load how many associated entries there are for
    // each category
    return customSelect(
      'SELECT *, (SELECT COUNT(*) FROM todos WHERE category = c.id) AS "amount" FROM categories c;',
      readsFrom: {todos, categories}, // used for the stream: the stream will update when either table changes
      ).watch().map((rows) {
        // we get list of rows here. We just have to turn the raw data from the row into a
        // CategoryWithCount. As we defined the Category table earlier, drift knows how to parse
        // a category. The only thing left to do manually is extracting the amount
        return rows
          .map((row) => CategoryWithCount(Category.fromData(row.data, this), row.readInt('amount')))
          .toList();
    });
  }

For custom selects, you should use the readsFrom parameter to specify from which tables the query is reading. When using a Stream, drift will be able to know after which updates the stream should emit items.

You can also bind SQL variables by using question-mark placeholders and the variables parameter:

Stream<int> amountOfTodosInCategory(int id) {
  return customSelect(
    'SELECT COUNT(*) AS c FROM todos WHERE category = ?',
    variables: [Variable.withInt(id)],
    readsFrom: {todos},
  ).map((row) => row.readInt('c')).watch();
}

Of course, you can also use indexed variables (like ?12) - for more information on them, see the sqlite3 documentation.

Custom update statements

For update and delete statements, you can use customUpdate. Just like customSelect, that method also takes a sql statement and optional variables. You can also tell drift which tables will be affected by your query using the optional updates parameter. That will help with other select streams, which will then update automatically.