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في هذا الدرس

name the four ways objects and tables do not fit together.

الموضوعات المخطط لها

• This gap is called the object-relational impedance mismatch.
• Identity: Java has == and equals; tables have a primary key.
• Inheritance: objects have subclasses; tables have no such thing, so you choose a layout.
• Associations: objects hold references (and can point both ways); tables use foreign keys (one direction, many-to-many needs a join table).
• Granularity: one object may hold nested value objects (Money), while a table row is flat.