added docs and more tests

docs/api/filtering.md

@@ -0,0 +1,71 @@
+# API Filtering
+
+The NetBox API supports robust filtering of results based on the fields of each model.
+Generally speaking you are able to filter based on the attributes (fields) present in
+the response body. Please note however that certain read-only or metadata fields are not
+filterable.
+
+Filtering is achieved by passing HTTP query parameters and the parameter name is the
+name of the field you wish to filter on and the value is the field value.
+
+E.g. filtering based on a device's name:
+```
+/api/dcim/devices/?name=DC-SPINE-1
+```
+
+## Multi Value Logic
+
+While you are able to filter based on an arbitrary number of fields, you are also able to
+pass multiple values for the same field. In most cases filtering on multiple values is
+implemented as a logical OR operation. A notible exception is the `tag` filter which
+is a logical AND. Passing multiple values for one field, can be combined with other fields.
+
+For example, filtering for devices with either the name of DC-SPINE-1 _or_ DC-LEAF-4:
+```
+/api/dcim/devices/?name=DC-SPINE-1&name=DC-LEAF-4
+```
+
+Filtering for devices with tag `router` and `customer-a` will return only devices with
+_both_ of those tags applied:
+```
+/api/dcim/devices/?tag=router&tag=customer-a
+```
+
+## Lookup Expressions
+
+Certain model fields also support filtering using additonal lookup expressions. This allows
+for negation and other context specific filtering.
+
+These lookup expressions can be applied by adding a suffix to the desired field's name.
+E.g. `mac_address__n`. In this case, the filter expression is for negation and it is seperated
+by two underscores. Below are the lookup expressions that are supported across different field
+types.
+
+### Numeric Fields
+
+Numeric based fields (ASN, VLAN ID, etc) support these lookup expressions:
+
+- `n` - not equal (negation)
+- `lt` - less than
+- `lte` - less than or equal
+- `gt` - greater than
+- `gte` - greater than or equal
+
+### String Fields
+
+String based (char) fields (Name, Address, etc) support these lookup expressions:
+
+- `n` - not equal (negation)
+- `ic` - case insensitive contains
+- `nic` - negated case insensitive contains
+- `isw` - case insensitive starts with
+- `nisw` - negated case insensitive starts with
+- `iew` - case insensitive ends with
+- `niew` - negated case insensitive ends with
+- `ie` - case sensitive exact match
+- `nie` - negated case sensitive exact match
+
+### Foreign Keys & Other Fields
+
+Certain other fields, namely foreign key relationships support just the negation
+expression: `n`.

docs/api/overview.md

@@ -62,6 +62,8 @@ Lists of objects can be filtered using a set of query parameters. For example, t
 GET /api/dcim/interfaces/?device_id=123
 ```
 
+See [filtering](filtering.md) for more details.
+
 # Serialization
 
 The NetBox API employs three types of serializers to represent model data: