Rewrote documentation for custom fields

docs/additional-features/custom-fields.md

@@ -1,26 +1,69 @@
 # Custom Fields
 
-Each object in NetBox is represented in the database as a discrete table, and each attribute of an object exists as a column within its table. For example, sites are stored in the `dcim_site` table, which has columns named `name`, `facility`, `physical_address`, and so on. As new attributes are added to objects throughout the development of NetBox, tables are expanded to include new rows.
+Each model in NetBox is represented in the database as a discrete table, and each attribute of a model exists as a column within its table. For example, sites are stored in the `dcim_site` table, which has columns named `name`, `facility`, `physical_address`, and so on. As new attributes are added to objects throughout the development of NetBox, tables are expanded to include new rows.
 
-However, some users might want to associate with objects attributes that are somewhat esoteric in nature, and that would not make sense to include in the core NetBox database schema. For instance, suppose your organization needs to associate each device with a ticket number pointing to the support ticket that was opened to have it installed. This is certainly a legitimate use for NetBox, but it's perhaps not a common enough need to warrant expanding the internal data schema. Instead, you can create a custom field to hold this data.
+However, some users might want to store additional object attributes that are somewhat esoteric in nature, and that would not make sense to include in the core NetBox database schema. For instance, suppose your organization needs to associate each device with a ticket number correlating it with an internal support system record. This is certainly a legitimate use for NetBox, but it's not a common enough need to warrant including a field for _every_ NetBox installation. Instead, you can create a custom field to hold this data.
 
-Custom fields must be created through the admin UI under Extras > Custom Fields. To create a new custom field, select the object(s) to which you want it to apply, and the type of field it will be. NetBox supports six field types:
+Within the database, custom fields are stored as JSON data directly alongside each object. This alleviates the need for complex queries when retrieving objects.
 
-* Free-form text (up to 255 characters)
-* Integer
-* Boolean (true/false)
-* Date
-* URL
-* Selection
+## Creating Custom Fields
 
-Assign the field a name. This should be a simple database-friendly string, e.g. `tps_report`. You may optionally assign the field a human-friendly label (e.g. "TPS report") as well; the label will be displayed on forms. If a description is provided, it will appear beneath the field in a form.
+Custom fields must be created through the admin UI under Extras > Custom Fields. NetBox supports six types of custom field:
 
-Marking the field as required will require the user to provide a value for the field when creating a new object or when saving an existing object. A default value for the field may also be provided. Use "true" or "false" for boolean fields. (The default value has no effect for selection fields.)
+* Text: Free-form text (up to 255 characters)
+* Integer: A whole number (positive or negative)
+* Boolean: True or false
+* Date: A date in ISO 8601 format (YYYY-MM-DD)
+* URL: This will be presented as a link in the web UI
+* Selection: A selection of one of several pre-defined custom choices
 
-When creating a selection field, you should create at least two choices. These choices will be arranged first by weight, with lower weights appearing higher in the list, and then alphabetically.
+Each custom field must have a name; this should be a simple database-friendly string, e.g. `tps_report`. You may also assign a corresponding human-friendly label (e.g. "TPS report"); the label will be displayed on web forms. A weight is also required: Higher-weight fields will be ordered lower within a form. (The default weight is 100.) If a description is provided, it will appear beneath the field in a form.
 
-## Using Custom Fields
+Marking a field as required will force the user to provide a value for the field when creating a new object or when saving an existing object. A default value for the field may also be provided. Use "true" or "false" for boolean fields, or the exact value of a choice for selection fields.
 
-When a single object is edited, the form will include any custom fields which have been defined for the object type. These fields are included in the "Custom Fields" panel. On the backend, each custom field value is saved separately from the core object as an independent database call, so it's best to avoid adding too many custom fields per object.
+The filter logic controls how values are matched when filtering objects by the custom field. Loose filtering (the default) matches on a partial value, whereas exact matching requires a complete match of the given string to a field's value. For example, exact filtering with the string "red" will only match the exact value "red", whereas loose filtering will match on the values "red", "red-orange", or "bored". Setting the filter logic to "disabled" disables filtering by the field entirely.
 
-When editing multiple objects, custom field values are saved in bulk. There is no significant difference in overhead when saving a custom field value for 100 objects versus one object. However, the bulk operation must be performed separately for each custom field.
+A custom field must be assigned to one or object types, or models, in NetBox. Once created, custom fields will automatically appear as part of these models in the web UI and REST API. Note that not all models support custom fields.
+
+### Custom Field Validation
+
+NetBox supports limited custom validation for custom field values. Following are the types of validation enforced for each field type:
+
+* Text: Regular expression (optional)
+* Integer: Minimum and/or maximum value (optional)
+* Selection: Must exactly match one of the prescribed choices
+
+### Custom Selection Fields
+
+Each custom selection field must have at least two choices. These are specified as a comma-separated list. Choices appear in forms in the order they are listed. Note that choice values are saved exactly as they appear, so it's best to avoid superfluous punctuation or symbols where possible.
+
+If a default value is specified for a selection field, it must exactly match one of the provided choices.
+
+## Custom Fields and the REST API
+
+When retrieving an object via the REST API, all of its custom data will be included within the `custom_fields` attribute. For example, below is the partial output of a site with two custom fields defined:
+
+```json
+{
+    "id": 123,
+    "url": "http://localhost:8000/api/dcim/sites/123/",
+    "name": "Raleigh 42",
+    ...
+    "custom_fields": {
+        "deployed": "2018-06-19",
+        "site_code": "US-NC-RAL42"
+    },
+    ...
+```
+
+To set or change these values, simply include nested JSON data. For example:
+
+```json
+{
+    "name": "New Site",
+    "slug": "new-site",
+    "custom_fields": {
+        "deployed": "2019-03-24"
+    }
+}
+```