drift/sqlparser

sqlparser

An sql parser and static analyzer, written in pure Dart. At the moment, only SELECT and DELETE statements are supported. Further, this library only targets the sqlite dialect at the time being.

Features

Not all features are available yet, put parsing select statements (even complex ones!) and performing analysis on them works!

Just parsing

You can parse the abstract syntax tree of sqlite statements with SqlEngine.parse.

import 'package:sqlparser/sqlparser.dart';

final engine = SqlEngine();
final result = engine.parse('''
SELECT f.* FROM frameworks f
  INNER JOIN uses_language ul ON ul.framework = f.id
  INNER JOIN languages l ON l.id = ul.language
WHERE l.name = 'Dart'
ORDER BY f.name ASC, f.popularity DESC
LIMIT 5 OFFSET 5 * 3
  ''');
// result.rootNode contains the select statement in tree form

Analysis

Given information about all tables and a sql statement, this library can:

1. Determine which result columns a query is going to have, including types and nullability
2. Make an educated guess about what type the variables in the query should have (it's not really possible to be 100% accurate about this because sqlite is very flexible at types)
3. Issue warnings about queries that are syntactically valid but won't run

To use the analyzer, first register all known tables via SqlEngine.registerTable. Then, SqlEngine.analyze(sql) gives you a AnalysisContext which contains an annotated ast and information about errors. The type of result columns and expressions can be inferred by using AnalysisContext.typeOf(). Here's an example.

final id = TableColumn('id', const ResolvedType(type: BasicType.int));
final content = TableColumn('content', const ResolvedType(type: BasicType.text));
final demoTable = Table(
  name: 'demo',
  resolvedColumns: [id, content],
);
final engine = SqlEngine()..registerTable(demoTable);

final context =
    engine.analyze('SELECT id, d.content, *, 3 + 4 FROM demo AS d');

final select = context.root as SelectStatement;
final resolvedColumns = select.resolvedColumns;

resolvedColumns.map((c) => c.name)); // id, content, id, content, 3 + 4
resolvedColumns.map((c) => context.typeOf(c).type.type) // int, text, int, text, int, int

But why?

Moor, a persistence library for Flutter apps, uses this package to generate type-safe methods from sql.

Limitations

• For now, only SELECT and DELETE expressions are implemented, UPDATE and INSERT will follow soon.
• Windowing is not supported yet
• Common table expressions and compound select statements UNION / INTERSECT are not supported and probably won't be in the near future.

Thanks

• To Bob Nystrom for his amazing "Crafting Interpreters" book, which was incredibly helpful when writing the parser.
• To the authors of SQLDelight. This library uses their algorithm for type inference.