There are two main ways to use the ORM: through automatic ORM properties, which automatically connects appropriately marked `DbArray` properties to the specified database, or by manually instantiating a `DbArray` with a `DbArrayBuilder`.
* [Automatic ORM properties example »](https://github.com/danog/AsyncOrm/blob/master/examples/1-automatic.php)
* [Manual example »](https://github.com/danog/AsyncOrm/blob/master/examples/2-manual.php)
The `DbArray` obtained through one of the methods above is an abstract array object that automatically stores and fetches elements of the specified [type »](#value-types), from the specified database.
`DbArray`s of type `ValueType::OBJECT` can contain objects extending `DbObject`.
Classes extending `DbObject` have a special `save` method that can be used to persist object changes to the database, as can be seen in the [example](https://github.com/danog/AsyncOrm/blob/master/examples/2-manual.php).
All these classes have multiple fields, described in their respective documentation (click on each class name to view it).
#### Caching
One of the most important settings is the `cacheTtl` field, which specifies the duration of the read and write cache.
If non-zero, all array elements fetched from the database will be stored in an in-memory *read cache* for the specified number of seconds; multiple accesses to the same field will each postpone flushing of that field by `cacheTtl` seconds.
All elements written to the array by the application will also be stored in an in-memory *write cache*, and flushed to the database every `cacheTtl` seconds.
If the array has an [object value type (ValueType::OBJECT)](#key-and-value-types), write caching is disabled.
If `cacheTtl` is 0, read and write caching is disabled.
A special setting class is used to create `DbArray`s backed by no database, which can also be useful in certain circumstances:
Each DbArray must have a specific key and value type.
For optimal performance, the specified types must be as strict as possible, here's a list of allowed types:
#### Key types
*`KeyType::STRING` - String keys only
*`KeyType::INT` - Integer keys only
*`KeyType::STRING_OR_INT` - String or integer keys (not recommended, for performance reasons please always specify either `STRING` or `STRING_OR_INT`).
#### Value types
*`ValueType::STRING`: Direct storage of UTF-8 string values.
*`ValueType::INT`: Direct storage of integer values.
*`ValueType::BOOL`: Direct storage of boolean values.
*`ValueType::FLOAT`: Direct storage of floating point (double precision) values.
*`ValueType::SCALAR`: Values of any scalar type (including arrays, excluding objects), serialized as specified in the settings.
Using SCALAR worsens performances, please use any of the other types if possible.
*`ValueType::OBJECT`: Objects extending DbObject, serialized as specified in the settings.
One of the most important value types is `ValueType::OBJECT`, it is used to store entire objects extending the `DbObject` class to the database.
Objects extending `DbObject` have a special `save` method that can be used to persist object changes to the database, as can be seen in the [example](https://github.com/danog/AsyncOrm/blob/master/examples/2-manual.php).
