Create JsonModelLoader

[oliwenmandiamond]

Create a json_model_loader factory function. Wraps load_json_file_to_class but allows for use of configuring defaults. Will be used with plans and BlueapiClient.

from blueapi.client import BlueapiClient
bc = BlueapiClient.from_config_file("/path/to/config.yaml")
...

from dodal.common.data_util import json_model_loader, JsonModelConfig
load_data = json_model_loader(MyModel, JsonModelConfig.from_default_file("/my/default/file.json"))
...

# Plans can't use file paths, so need to be loaded on client side and data passed
# through via pydantic model.
bc.plan.my_plan(det1, load_data()) # Uses configured default file.
bc.plan.my_plan(det1, load_data("/path/to/data.json")) # Use absolute path
bc.plan.my_plan(det1, load_data("data.json")) # Use relative path

Instructions to reviewer on how to test:

1. Check tests pass.
2. Implementation makes sense.

Checks for reviewer

• Would the PR title make sense to a scientist on a set of release notes
• If a new device has been added does it follow the standards
• If changing the API for a pre-existing device, ensure that any beamlines using this device have updated their Bluesky plans accordingly
• Have the connection tests for the relevant beamline(s) been run via dodal connect ${BEAMLINE}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.08%. Comparing base (052b80a) to head (441bb61).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1934      +/-   ##
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+ Coverage   99.05%   99.08%   +0.02%     
==========================================
  Files         314      314              
  Lines       11778    11801      +23     
==========================================
+ Hits        11667    11693      +26     
+ Misses        111      108       -3     

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[tpoliaw]

There isn't really anything wrong with the implementation but couldn't the same thing be done with a local function?

def load_data(file: str = DEFAULT) -> MyModel:
    return load_json_file_to_class(MyModel, file)

bc.plans.my_plan(det1, load_data())
bc.plans.my_plan(det1, load_data("path/to/data.json"))

As models are going to be serialized back to JSON and then reconstructed and validated on the server, it might be easier to read straight to JSON and pass it directly. At the moment the data is going file -> str -> json -> model -> json -> model where the two models aren't necessarily the same version.

def load_data(file: str = DEFAULT):
    with open(file) as src:
        return json.load(src)

I might have missed something though, is there a use case within plans where this would offer something more?

[oliwenmandiamond]

There isn't really anything wrong with the implementation but couldn't the same thing be done with a local function?

def load_data(file: str = DEFAULT) -> MyModel:
    return load_json_file_to_class(MyModel, file)

bc.plans.my_plan(det1, load_data())
bc.plans.my_plan(det1, load_data("path/to/data.json"))

Yes, I could do this

def p60_load_sequence(file: str) -> P60Sequence: 
     return load_json_file_to_class(P60Sequence, file) 

...
def i09_load_sequence(file: str) -> I09Sequence: 
    return load_json_file_to_class(I09Sequence, file) 

...
def i09_1_load_sequence(file: str) -> I091Sequence: 
    return load_json_file_to_class(I091Sequence, file) 

...
def b07_load_sequence(file: str) -> B07BSequence: 
    return load_json_file_to_class(B07BSequence, file)

...
def b07_1_load_sequence(file: str) -> B07CSequence: 
    return load_json_file_to_class(B07CSequence, file)

for each specific beamline. However, I wanted a standard way to do this via configuration rather defining a new function in the environment every time. This also means it is fully tested, has documentation, and can also reused with existing tests within dodal and plan repos rather than redefining a new loader function for each test.

As models are going to be serialized back to JSON and then reconstructed and validated on the server, it might be easier to read straight to JSON and pass it directly. At the moment the data is going file -> str -> json -> model -> json -> model where the two models aren't necessarily the same version.

def load_data(file: str = DEFAULT):
    with open(file) as src:
        return json.load(src)

I might have missed something though, is there a use case within plans where this would offer something more?

So I know the type checking isn't added yet, but when it is added surely this will provide the type checking for the model? E.g the model on client side and server side have to match?

def my_plan(model: MyModel1, ...):
     ...

load_model1 = JsonModelLoader[MyModel1](MyModel1)
load_model2 = JsonModelLoader[MyModel2](MyModel2)
...
bc.plans.my_plan(load_model1("/my/file")) # Okay
bc.plans.my_plan(load_model2("/my/file")) # Static type checker should complain as it isn't using the correct model?

[tpoliaw]

So I know the type checking isn't added yet, but when it is added surely this will provide the type checking for the model? E.g the model on client side and server side have to match?

Unfortunately not. The client is working entirely from the API schema provided by the server. For a plan that accepts MyModel, the schema only contains a list of fields that the model should have, it has no information about the source of the model. The PR for the offline client typing currently only uses Any for complex models as everything gets validated on the server.

You can see the spec the client has available by running blueapi controller -o json plans.

[tpoliaw]

However, I wanted a standard way to do this via configuration

It's not really any different but if you want to avoid writing a function you could do

def json_model_loader(model: type[TBaseModel], default_file: str|None=None):
    def load_json(file: str| None = default_file) -> TBaseModel:
        if file is None:
            raise ValueError("No filename given")
        return load_json_file_to_class(bm, file)
    return load_json

and then your example becomes

p60_load_sequence = json_model_loader(P60Sequence, file) 

i09_load_sequence = json_model_loader(I09Sequence, file) 

which isn't really that different to (and if anything is clearer than)

p60_load_sequence = JsonModelLoader[P60Sequence](P60Sequence, "my/default/file.json")

i09_load_sequence = JsonModelLoader[I09Sequence](I09Sequence, "my/default/file.json")

[oliwenmandiamond]

However, I wanted a standard way to do this via configuration

It's not really any different but if you want to avoid writing a function you could do

def json_model_loader(model: type[TBaseModel], file: str|None=None):
    def load_json(file: str| None) -> TBaseModel:
        if file is None:
            raise ValueError("No filename given")
        return load_json_file_to_class(bm, file)
    return load_json

and then your example becomes

p60_load_sequence = json_model_loader(P60Sequence, file) 

i09_load_sequence = json_model_loader(I09Sequence, file) 

which isn't really that different to (and if anything is clearer than)

p60_load_sequence = JsonModelLoader[P60Sequence](P60Sequence, "my/default/file.json")

i09_load_sequence = JsonModelLoader[I09Sequence](I09Sequence, "my/default/file.json")

With a small tweak, I do like how simple your function is

def json_model_loader(model: type[TBaseModel], default_file: str | None = None):
    def load_json(file: str | None = None) -> TBaseModel:
        if file is None and default_file is not None:
            return load_json_file_to_class(model, default_file)
        elif file is not None:
            return load_json_file_to_class(model, file)
        raise RuntimeError(
            f"{model.__name__} loader has no default file configured and no file was"
            "provided when trying to load in a model. "
        )
   return load_json

However, I am not sure it is correct approach because it is quite limiting. For example, I cannot view or update the default file at a later date, I have to rerun the factory function again and reassign to the variable for my function which I'm not sure I like

[tpoliaw]

When would you need to check or modify the default value? Isn't the point that you can override it if you want a different value?

Also, I posted my example function without checking it properly, I think if you use

def json_model_loader(model: type[TBaseModel], default_file: str|None=None):
    def load_json(file: str| None = default_file) -> TBaseModel:
        if file is None:
            raise ValueError("No filename given")
        return load_json_file_to_class(bm, file)
    return load_json

you get the default file behaviour you're after.

[oliwenmandiamond]

When would you need to check or modify the default value? Isn't the point that you can override it if you want a different value?

I was thinking of just trying to make it flexible enough. However, if we need it we can cross that bridge when we get there. I have update it to use your implementation so ready for review