Empty value handling

When deleting a field value from a custom database table — either by passing an empty value to update_field() or by invoking delete_field() — the data type must be considered to ensure the table column receives the correct 'empty' value. This is especially true when controlling column data types for maximum efficiency.

For example, a string type requires an empty string whereas numerical and date types require a NULL value to effectively clear the field. The plugin handles this for you but there may be situations where you require control over this behaviour. For this reason, a collection of filters are available that allow you to control:

1. Whether an incoming value should be considered empty — this will result in an empty table column.
2. The value that should be used as an empty value when updating a particular data type.
3. The value that should be used as an empty value when updating a particular field.

Controlling whether an incoming value should be considered empty

By default, the plugin considers empty strings and null to be empty values. This is in line with WordPress' core meta handling system and maintains behaviour consisten with ACF. However, there may be other values you wish to result in an empty column.

An example of this might be when passing an empty array to update_field() when updating a relationship field. When saved to the database, the empty array is serialized in core metatables, and is JSON encoded in custom DB tables. Both data stores have an equivalent string representation of an empty array.

The following example demonstrates how to configure relationship fields with empty arrays to store an empty value in custom database tables:

Be sure to be test thoroughly when checking for empty values. Avoid using empty() unless it is exactly what you are after as empty( 0 ) === TRUE and this can result in empty values when a field actually contains a zero.

Specifying the empty value for a particular field

You may specify which value should be used for a given field to represent an empty value. This value is intended for use to clear the table value for the field in question but may also be used to specify alternative values when necessary.

Specifying the empty value for a particular data type

You may specify which value should be used for a given SQL data type to represent an empty value. This value is intended for use to clear the table value for any field with a specific data type.