Example 4 - Using get or update helpers

This example aims to expand on Example 1 that will take advantage of two new helper methods on the Adapter class; get_or_instantiate and update_or_instantiate.

Both methods act similar to Django's get_or_create function to return the object and then a boolean to identify whether the object was created or not. Let's dive into each of them.

get_or_instantiate

The following arguments are supported: model (DiffSyncModel), ids (dictionary), and attrs (dictionary). The model and ids are used to find an existing object. If the object does not currently exist within the Adapter adapter, it will then use model, ids, and attrs to add the object.

It will then return a tuple that can be unpacked.

obj, created = self.get_or_instantiate(Interface, {"device_name": "test100", "name": "eth0"}, {"description": "Test description"})

If the object already exists, created will be False or else it will return True if the object had to be created.

update_or_instantiate

This helper is similar to get_or_instantiate, but it will update an existing object or add a new instance with the provided ids and attrs. The method does accept the same arguments, but requires attrs, whereas get_or_instantiate does not.

obj, created = self.update_or_instantiate(Interface, {"device_name": "test100", "name": "eth0"}, {"description": "Test description"})

Example Walkthrough

We can take a look at the data we will be loading into each backend to understand why these helper methods are valuable.

Example Data

BACKEND_DATA_A = [
    {
        "name": "nyc-spine1",
        "role": "spine",
        "interfaces": {"eth0": "Interface 0", "eth1": "Interface 1"},
        "site": "nyc",
    },
    {
        "name": "nyc-spine2",
        "role": "spine",
        "interfaces": {"eth0": "Interface 0", "eth1": "Interface 1"},
        "site": "nyc",
    },
]

Example Load

    def load(self):
        """Initialize the BackendA Object by loading some site, device and interfaces from DATA."""
        for device_data in BACKEND_DATA_A:
            device, instantiated = self.get_or_instantiate(
                self.device, {"name": device_data["name"]}, {"role": device_data["role"]}
            )

            site, instantiated = self.get_or_instantiate(self.site, {"name": device_data["site"]})
            if instantiated:
                device.add_child(site)

            for intf_name, desc in device_data["interfaces"].items():
                intf, instantiated = self.update_or_instantiate(
                    self.interface, {"name": intf_name, "device_name": device_data["name"]}, {"description": desc}
                )
                if instantiated:
                    device.add_child(intf)

The new methods are helpful due to having devices that are part of the same site. As we iterate over the data and load it into the Adapter adapter, we would have to account for ObjectAlreadyExists exceptions when we go to add each duplicate site we encounter within the data or possibly several other models depending how complex the synchronization of data is between backends.