TablePerHierarchy

TablePerHierarchy (TPH) is a strategy used in object-relational mapping (ORM) to map an inheritance hierarchy to a single database table. In TPH, all classes in the hierarchy are stored in a single table, with a discriminator column used to distinguish between different types of objects. This column typically contains values that indicate the specific subclass to which each row belongs.

TPH is particularly useful when dealing with a small number of subclasses, as it avoids the need for complex joins and can simplify queries. However, it may not be suitable for large inheritance hierarchies, as it can lead to a table with many columns, some of which may be unused for certain subclasses.

The main advantage of TPH is its simplicity and ease of use. It requires minimal configuration and can be easily implemented in most ORM frameworks. Additionally, TPH can improve performance by reducing the number of joins required to retrieve data.

However, TPH also has some limitations. It can lead to a table with many columns, some of which may be unused for certain subclasses. This can result in wasted storage space and may make the table more difficult to manage. Additionally, TPH may not be suitable for large inheritance hierarchies, as it can lead to a table with many columns, some of which may be unused for certain subclasses.

In summary, TablePerHierarchy is a useful strategy for mapping an inheritance hierarchy to a single database table, particularly when dealing with a small number of subclasses. However, it may not be suitable for large inheritance hierarchies, and it may lead to a table with many columns, some of which may be unused for certain subclasses.