Migrating Smart Segments - Forest Documentation

Smart segments migrate quickly. The syntax is very similar to the legacy agent. The main difference is in the return value.

What changed

Because the new agent is designed to work with multiple databases, the return value of the segment handler is no longer a Sequelize/Mongoose condition. Instead, you build a condition tree that the agent translates to the appropriate database syntax.

API cheatsheet (Node.js)

Legacy agent	New agent
`where:`	handler body (return value)
`sequelize.where(...)`	condition tree `{ field, operator, value }`

Performance tip

Many queries map directly to Forest condition trees, giving much better performance than performing the query yourself and then building a naive id IN (...) condition.

Example

Before (Node.js)
After (Node.js)
Before (Ruby)
After (Ruby)

collection('products', {
  segments: [{
    name: 'Bestsellers',
    where: async product => {
      const query = `
        SELECT products.id, COUNT(orders.*)
        FROM products
        JOIN orders ON orders.product_id = products.id
        GROUP BY products.id
        ORDER BY count DESC
        LIMIT 5;
      `;
      const products = await models.connections.default.query(query, {
        type: QueryTypes.SELECT,
      });
      return { id: { [Op.in]: products.map(p => p.id) } };
    },
  }],
});

agent.customizeCollection('products', products => {
  products.addSegment('Bestsellers', async () => {
    const query = `
      SELECT products.id, COUNT(orders.*)
      FROM products
      JOIN orders ON orders.product_id = products.id
      GROUP BY products.id
      ORDER BY count DESC
      LIMIT 5;
    `;
    const products = await models.connections.default.query(query, {
      type: QueryTypes.SELECT,
    });
    return { field: 'id', operator: 'In', value: products.map(p => p.id) };
  });
});

class Forest::Product
  include ForestLiana::Collection
  collection :Product

  segment 'Bestsellers' do
    query = <<~SQL
      SELECT products.id, COUNT(orders.*)
      FROM products
      JOIN orders ON orders.product_id = products.id
      GROUP BY products.id
      ORDER BY count DESC
      LIMIT 5;
    SQL
    products = ActiveRecord::Base.connection.execute(query)
    { id: products.map { |p| p['id'] } }
  end
end

@create_agent.customize_collection('product') do |collection|
  collection.add_segment('best_sellers') do |context|
    rows = ActiveRecord::Base.connection.execute(
      'SELECT products.id as product_id, COUNT(orders.id) as nb
       FROM products
       INNER JOIN orders ON orders.product_id = products.id
       GROUP BY products.id
       ORDER BY nb DESC
       LIMIT 5;'
    )
    {
      field: 'id',
      operator: 'In',
      value: rows.map { |r| r['product_id'] }
    }
  end
end

​What changed

​API cheatsheet (Node.js)

​Performance tip

​Example

What changed

API cheatsheet (Node.js)

Performance tip

Example