Free web space - The Hibernate type system You ve probably noticed that
The Hibernate type system You ve probably noticed that your database doesn t support some of the SQL types mentioned in table 5.1. The listed type names are names of ANSI-standard datatypes. Most database vendors ignore this part of the SQL standard (because their legacy type systems often predate the standard). However, the JDBC driver provides a partial abstraction of vendor-specific SQL datatypes, allowing Hibernate to work with ANSI-standard types when executing DML. For database-specific DDL generation, Hibernate translates from the ANSI-standard type to an appropriate vendor-specific type, using the built-in support for specific SQL dialects. (This means you usually don t have to worry about SQL datatypes if you re using Hibernate for data access and SQL schema definition.) Furthermore, the Hibernate type system is smart and can switch SQL datatypes depending on the defined length of a value. The most obvious case is string: If you declare a string property mapping with a length attribute, Hibernate picks the correct SQL datatype depending on the selected dialect. For MySQL, for example, a length of up to 65535 results in a regular VARCHAR(length) column when Hibernate exports the schema. For a length of up to 16777215, a MEDIUMTEXT datatype is used. Larger string mappings result in a LONGTEXT. Check your SQL dialect (the source code comes with Hibernate) if you want to know the ranges for this and other mapping types. You can customize this behavior by sub- classing your dialect and overriding these settings. Most dialects also support setting the scale and precision of decimal SQL datatypes. For example, a precision or scale setting in your mapping of a Big- Decimal creates a NUMERIC(precision, scale) datatype for MySQL. Finally, the yes_no and true_false mapping types are converters that are mostly useful for legacy schemas and Oracle users; Oracle DBMS products don t have a built-in boolean or truth-valued type (the only built-in datatype actually required by the relational data model). Date and time mapping types Table 5.2 lists Hibernate types associated with dates, times, and timestamps. In your domain model, you may choose to represent date and time data using java.util.Date, java.util.Calendar, or the subclasses of java.util.Date defined in the java.sql package. This is a matter of taste, and we leave the decision to you make sure you re consistent, however. (In practice, binding your domain model to types from the JDBC package isn t the best idea.) A caveat: If you map a java.util.Date property with timestamp (the most common case), Hibernate returns a java.sql.Timestamp when loading the property from the database. Hibernate has to use the JDBC subclass because it includes
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