how-to-export-sqlite-tables-to-create-statements（如何导出 sqlite 表来创建语句）

How to Export SQLite Tables to CREATE Statements

In this article I will show you how to export all the tables and indexes in a SQLite database to CREATE statements at runtime.

Getting started

Start by creating a new directory and Flutter project:

mkdir sqlite_introspect
cd sqlite_introspect
flutter create .
flutter pub add sqlite3 mustache_template

This will add the sqlite3 package which uses FFI to call the native executable and mustache that we will use for templates later.

Creating the database

Creating the database can be done either in memory or based on a local file. For this example we will use in memory:

final Database db = sqlite3.openInMemory();

Don't forget to dispose of the database after use:

db.dispose();

Defining the template

Since we will be using Mustache we can define the variables that we will pass to the template as JSON.

Create a TableInfo class that will store the fields and indexes:

class TableInfo {
  final String name;
  final List<Map<String, dynamic>> fields;
  final List<Map<String, dynamic>> indexes;

  TableInfo({
    required this.name,
    required this.fields,
    required this.indexes,
  });

  Map<String, dynamic> toJson() {
    return {
      'name': name,
      'fields': [
        for (var i = 0; i < fields.length; i++)
          {
            'index': i,
            'table': name,
            'isLast': i == fields.length - 1,
            ...fields[i],
          },
      ],
      'indexes': [
        for (var i = 0; i < indexes.length; i++)
          {
            'index': i,
            'table': name,
            'isLast': i == indexes.length - 1,
            ...indexes[i],
          },
      ],
    };
  }
}

Now we can create the Mustache template used to build up the CREATE statements:

const template = '''
{{#tables}}
CREATE TABLE {{name}} (
  {{#fields}}
  {{name}} {{#type}} {{.}}{{/type}}{{#notnull}} NOT NULL{{/notnull}}{{#pk}} PRIMARY KEY{{/pk}}{{#dflt_value}} DEFAULT {{.}}{{/dflt_value}}{{^isLast}},{{/isLast}}
  {{/fields}}
);
{{#indexes}}
CREATE {{#unique}} UNIQUE{{/unique}} {{name}}
ON {{table}}({{#values}} {{name}} {{/values}}{{^isLast}},{{/isLast}});
{{/indexes}}
{{/tables}}
''';

Exporting the PRAGMA

Now we can export the PRAGMA for the database by exporting the list of tables, querying the column information and indexes about each one.

final tables = <TableInfo>[];
// Export table names
final tableNames = db
	.select("SELECT name FROM sqlite_master WHERE type='table';")
	.map((e) => e['name'] as String);
for (final t in tableNames) {
  // Export column information
  final info = db.select('PRAGMA table_info($t);');
  final tbl = TableInfo(name: t, fields: [], indexes: []);
  for (final c in info) {
    tbl.fields.add(c);
  }
  // Export index names
  final indexList = db.select('PRAGMA index_list($t);');
  for (final index in indexList) {
    final name = index['name'] as String;
    // Export index information
    final infos = db.select('PRAGMA index_info($name);');
    final indexValue = {...index, 'values': infos};
    tbl.indexes.add(indexValue);
  }
  tables.add(tbl);
}

Rendering the template

Now take the tables we just exported and pass them to the mustache template to render:

final tml = Template(template);
final args = {"tables": tables.map((e) => e.toJson()).toList()};
final str = tml.renderString(args);
print(str);

This will now print out all the tables and indexes as CREATE as valid SQL. 🎉