Custem Fields allow to set json-structured data as default value, but instances using the custom_field can only set strings

[reduzent]

I would like to define a CustomField for the object type Prefix named dhcp_option_domain_name_servers that has the default set to structured data, specifically a list:

[
    "10.158.0.53", 
    "10.158.1.53"
]

When I access the CustomField dhcp_option_domain_name_servers in an export template, I can iterate over the list:

name-servers: {{ ', '.join(prefix.cf.get('dhcp_option_domain_name_servers')) }}

-->

name-servers: 10.158.0.53, 10.158.1.53

However, when I set the CustomField dhcp_option_domain_name_servers for a specific instance of a Prefix to the value:

[
    "10.157.0.53", 
    "10.157.1.53"
]

the value seems to be saved as string and not structured data. The same export template from above returns:

name-servers: [, ", 1, 0, ., 1, 5, 7, ., 0, ., 5, 3, ", ,,  , ", 1, 0, ., 1, 5, 8, ., 1, ., 5, 3, ", ]

[reduzent]

Instances seem to be able to save their custom field data only as string in the database. That's how it looks for an instance that uses the default:

(from select custom_field_data from ipam_prefix where id = 1;)

{"dhcp_option_domain_name_servers": ["10.158.0.53", "10.158.1.53"]}

That's how it looks for an instance that saved its own value:

(from select custom_field_data from ipam_prefix where id = 4;)

{"dhcp_option_domain_name_servers": "[\"10.157.0.53\", \"10.157.1.53\"]"

[reduzent]

Is this a bug or am I misunderstanding the design of custom fields?

[reduzent]

Sorry for not being clear. I try again.

This is with

• netbox 3.4.6
• Python 3.9.2

Steps to reproduce the issue

1. Create new Custom Field:
   • Content Type: IPAM > Prefix
   • Name: dhcp_option_domain_name_servers
   • Default value: ["10.158.0.53", "10.158.1.53"]
2. Create Prefix:
   • Prefix: 10.158.0.0/24
   • Leave custom field dhcp_option_domain_name_servers at default value
3. Create another Prefix:
   • Prefix: 10.157.100.0/24
   • Set custom field dhcp_option_domain_name_servers to ["10.157.0.53", "10.157.1.53"]
4. Create Export template:
   • Name: nameservsers
   • Content Type: IPAM > Prefix
   • Template:

{%- for prefix in  queryset %}
- prefix: {{ prefix }}
  nameservers: {{ ', '.join(prefix.cf.get('dhcp_option_domain_name_servers')) }}
{% endfor %}

4. Access the new export template with curl:
   • curl -H "Authorization: Token XXX" "https://example.com/api/ipam/prefixes/?export=nameservers"

Result:

- prefix: 10.158.0.0/24
  nameservers: 10.158.0.53, 10.158.1.53

- prefix: 10.157.100.0/24
  nameservers: [, ", 1, 0, ., 1, 5, 7, ., 0, ., 5, 3, ", ,,  , ", 1, 0, ., 1, 5, 7, ., 1, ., 5, 3, ", ]

Expected result:

- prefix: 10.158.0.0/24
  nameservers: 10.158.0.53, 10.158.1.53

- prefix: 10.157.100.0/24
  nameservers: 10.157.0.53, 10.157.1.53

[kkthxbye-code]

Create new Custom Field:
Content Type: IPAM > Prefix
Name: dhcp_option_domain_name_servers
Default value: ["10.158.0.53", "10.158.1.53"]

What type? If you are trying to put json data into a string custom field, that's your issue. If it's a string field, you are also using the default value wrong, it should be "[\"10.158.0.53\", \"10.158.1.53\"]" I think. You obviously wouldn't be able to access it as json though, you would have to parse it yourself.

If you are using a JSON custom field (which sounds like is actually what you want) it should work, works fine here at least.

[reduzent]

Where can I set the type of the custom field to JSON?

See here available options:

[kkthxbye-code]

That field should be scrollable.

[reduzent]

Thanks! That clears everything up for me!

[reduzent]

As @kkthxbye-code suggested correctly, type JSON is what I wanted to use. I was simply not seeing that the list of available types is scrollable.

🤦