Doctrine 2 vs Propel ORM: What are the differences?

# Introduction
In the world of PHP, two popular Object-Relational Mapping (ORM) tools are Doctrine 2 and Propel ORM. While both serve the purpose of mapping database tables to PHP objects, there are key differences that set them apart.

1. **Architecture**:
Doctrine 2 follows the Data Mapper pattern, where the domain objects are not responsible for their own persistence logic, while Propel uses the Active Record pattern, where the domain objects themselves handle interactions with the database.

2. **Query Language**:
Doctrine 2 uses DQL (Doctrine Query Language), which is object-oriented and designed for complex queries with joins and subqueries. In contrast, Propel ORM offers a query-building mechanism that resembles SQL and allows for easier integration and migration from traditional SQL queries.

3. **Mapping Strategy**:
Doctrine 2 employs XML, YAML, or annotations to define the mappings between database tables and PHP objects, providing flexibility and ease in configuration. Propel ORM, on the other hand, primarily uses XML for mapping, offering a more structured approach to defining database mappings.

4. **Community Support**:
Doctrine 2 has a larger and more active community compared to Propel ORM, providing extensive documentation, tutorials, and community support forums. Propel ORM, while having a dedicated user base, might have slightly fewer resources and support options available.

5. **Performance**:
Doctrine 2 is known for its advanced caching mechanisms and lazy loading capabilities, which can improve performance in scenarios with complex object graphs. Propel ORM, while efficient, may not offer the same level of performance optimizations out of the box.

6. **Tooling and Integration**:
Doctrine 2 offers robust integration with Symfony and other PHP frameworks, with a wide range of tools and plugins available for seamless development. Propel ORM, while compatible with various frameworks, might require additional configurations or adaptations for full integration.

# Summary
In summary, the key differences between Doctrine 2 and Propel ORM lie in their architecture, query language, mapping strategies, community support, performance optimizations, and tooling/integration options.