createContextFromSelect method

Implementation

GenerationContext createContextFromSelect(BaseSelectStatement select,
    Map<Column, Expression> columns, InsertMode mode,
    {UpsertClause<T, D>? onConflict}) {
  // To be able to reference columns by names instead of by their index like
  // normally done with `INSERT INTO SELECT`, we use a CTE. The final SQL
  // statement will look like this:
  // WITH source AS $select INSERT INTO $table (...) SELECT ... FROM source
  final ctx = GenerationContext.fromDb(database);
  const sourceCte = '_source';

  ctx.buffer.write('WITH $sourceCte AS (');
  select.writeInto(ctx);
  ctx.buffer.write(') ');

  final columnNameToSelectColumnName = <String, String>{};
  columns.forEach((key, value) {
    final name = select._nameForColumn(value);
    if (name == null) {
      throw ArgumentError.value(
          value,
          'column',
          'This column passd to insertFromSelect() was not added to the '
              'source select statement.');
    }

    columnNameToSelectColumnName[key.name] = name;
  });

  mode.writeInto(ctx);
  ctx.buffer
    ..write(' INTO ${ctx.identifier(table.aliasedName)} (')
    ..write(columnNameToSelectColumnName.keys.map(ctx.identifier).join(', '))
    ..write(') SELECT ')
    ..write(
        columnNameToSelectColumnName.values.map(ctx.identifier).join(', '))
    ..write(' FROM $sourceCte');
  if (onConflict != null) {
    // Resolve parsing ambiguity (a `ON` from the conflict clause could also
    // be parsed as a join).
    ctx.buffer.write(' WHERE TRUE');
    _writeOnConflict(ctx, mode, null, onConflict);
  }

  return ctx;
}