ejb-ql

In Container-Managed Persistence (CMP), the developer does not write SQL in Java code. The container generates persistence code automatically, but it still needs to know how to query the database. Without a query language, there’s no way to define finder queries in CMP without falling back to writing raw SQL in the bean class.

EJB-QL is an object-oriented query language used in CMP deployment descriptors to define finder and select queries. Unlike SQL which operates on tables and columns, EJB-QL operates on EJB abstract persistent fields and relationships.

1. Queries are written in ejb-jar.xml deployment descriptor, not in Java code
2. Syntax: SELECT OBJECT(p) FROM PRODUCTS p WHERE p.basePrice > ?1
3. p represents the bean abstract schema, not a database table
4. ?1 is a positional parameter passed from the finder method
5. Queries are parsed by the container and converted to actual SQL at deployment or runtime
6. Because XML uses < and > for tags, comparison operators must be wrapped in <![CDATA[ ... ]]> to avoid parser errors

• Object-oriented: operates on bean abstract schema names, not table/column names
• Defined in deployment descriptor, not Java source code
• Supports positional parameters (?1, ?2, etc.) for parameterized queries
• Requires CDATA wrapping for comparison operators in XML
• Container translates EJB-QL to vendor-specific SQL

• Built from: CMP — EJB-QL is exclusive to CMP beans
• Builds into: CMP Abstract Accessors — EJB-QL queries are used by finder methods defined via abstract accessors
• Contrasts with: SQL — EJB-QL is object-based and in XML; SQL is table-based and in Java code (BMP)
• Related: EJB Deployment Descriptor — EJB-QL queries live inside the deployment descriptor
• Related: CDATA Hack — XML escaping needed for EJB-QL operators

• Forgetting CDATA wrapping causes XML parsing errors on operators like >, <, >=
• EJB-QL syntax differs from JPQL (Java Persistence Query Language) in later JPA specs
• EJB-QL only works with CMP 2.0+ entity beans; BMP beans use raw JDBC
• Queries are validated at deployment time, not at compile time