Object relationship mapping definition

database - What is an ORM and where can I learn more about it? - Stack Overflow

object relationship mapping definition

"Object-Relational Mapping": In WebObjects, a system for transforming Entity- Relationship models to an object-oriented programming framework. Enterprise. Object-relational mapping in computer science is a programming technique for converting data between incompatible type systems using object-oriented. We already saw one example of Kodo JDO's object-relational mapping tools when Classes or fields whose mappings no longer match the class definition or .

It abstracts the DB system, so you can change it whenever you want.

Introduction to Object-Relational Mapping

The model is weakly bound to the rest of the application, so you can change it or use it anywhere else. It lets you use OOP goodness like data inheritance without a headache.

But ORM can be a pain: You have to learn it, and ORM libraries are not lightweight tools; You have to set it up.

object relationship mapping definition

It abstracts the DB. While it's OK if you know what's happening behind the scene, it's a trap for new programmers that can write very greedy statements, like a heavy hit in a for loop.

How to learn about ORM? Whichever ORM library you choose, they all use the same principles. There are a lot of ORM libraries around here: Propel or Doctrine I prefer the last one. If you want to try an ORM library in Web programming, you'd be better off using an entire framework stack like: Django Python, using a internal ORM.

Use this option to write the planned schema to an XML document rather than modify the data store. The document can then be manipulated and committed to the database with the schema tool.

Use this option to write the planned schema modifications to a SQL script rather than modify the data store.

  • Object-Relational Mapping (OR Mapping) Definition

Combine this with a schemaAction of build to generate a script that recreates the schema for the current mappings, even if the schema already exists.

Corresponds to the same-named option on the schema tool. This option is ignored if readSchema is not set to true.

What is Object/Relational Mapping? - Hibernate ORM

Set this option to true to read the entire existing schema when the tool runs. Reading the existing schema ensures that Kodo does not generate any mappings that use table, index, primary key, or foreign key names that conflict with existing names. Depending on the JDBC driver, though, it can be a very slow process for large schemas. Whether to read and manipulate primary key information of existing tables.

Defaults to false unless the readSchema flag is set to true. Whether to read and manipulate foreign key information of existing tables. This means that if you add a jdbc-delete-action extension to a field of a class that has already been mapped once, you must explicitly set this flag to true to have Kodo create the new foreign key on the existing table.

object relationship mapping definition

Whether to read and manipulate index information of existing tables. This means that if you add a jdbc-indexed extension to a field of a class that has already been mapped once, you must explicitly set this flag to true to have Kodo create the new index on the existing table. The available actions are: Bring the mapping information up-to-date with the class definitions. Remove the mapping information for the given classes.

Validate that the mappings for the given classes are valid and that they match the schema. No mappings or tables will be changed; an exception will be thrown if any mappings are invalid. Create the schema based on the existing mappings for the given classes. Revert the mappings for the given classes to their previously saved state. Some mapping factories may not be able to revert mapping data. Import mapping information from the given XML document and add it to the stored system mappings.

Export the mapping data for the given classes to an XML file. Each additional argument to the tool should be either the full name of a persistent class, the. If the import action is used, however, then any additional arguments will be interpreted as XML mapping data files.

What is Object-Relational Mapping (ORM)? - Definition from Techopedia

The mapping data generated by the mapping tool is stored in the system mapping factory. As you will see later in this chapter, you have several mapping factories to choose from. Thus, mapping data might end up stored in the database, in special mapping files, in JDO metadata vendor extensions, or in another format of your choosing. Using the Mapping Tool There are three primary approaches to object-relational mapping: The mapping tool has actions to facilitate each approach.

Object-relational mapping

In the object-to-schema approach to mapping, you concentrate your efforts on your object model, and the mapping tool's refresh action keeps your mappings and schema up-to-date. The refresh action examines both the existing database schema and any existing mapping information. Classes and fields that are not mapped, or whose mapping information no longer matches the object model or the schema, are automatically given new mappings.

The tool also updates the schema as necessary to support these new mappings. The example below shows how to invoke the refresh action on the mapping tool to create or update the mapping information and database schema for the persistent classes listed in package.

Refreshing Mappings and the Relational Schema mappingtool -a refresh package.