Ability to include private or "_" fields as part of the model.

[mdgilene]

Feature Request

Output of python -c "import pydantic.utils; print(pydantic.utils.version_info())":

             pydantic version: 1.4
            pydantic compiled: False
                 install path: C:\Anaconda3_2019.10\envs\test-env\Lib\site-packages\pydantic
               python version: 3.6.8 |Anaconda, Inc.| (default, Feb 21 2019, 18:30:04) [MSC v.1916 64 bit (AMD64)]
                     platform: Windows-10-10.0.17134-SP0
     optional deps. installed: ['email-validator']

When building models that are meant to add typing and validation to 3rd part APIs (in this case Elasticsearch) sometimes field names are prefixed with _ however these are not private fields that should be ignored and users may want them included in the model.

from pydantic import BaseModel

class ElastisearchRequest(BaseModel):
    _source: dict = Field(...)
    
    class Config:
        include_private_fields = True

request = ElasticsearchRequest(_source={'include': ['text']})

print(request.dict())

Output:

{
  "_source": {
    "include": ["text"]
  }
}

[samuelcolvin]

Duplicate of #655.

[StephenBrown2]

With MongoDB, which has an _id field, I usually just alias it, like:

from pydantic import BaseModel, Field

class MongoResponse(BaseModel):
    id: str = Field(..., alias="_id")
    
    class Config:
        allow_population_by_field_name = True

response = MongoResponse(_id="ThisIsAnId")

print(response.dict())

Output:

{'id': 'ThisIsAnId'}

So with your example:

from pydantic import BaseModel, Field

class ElasticsearchRequest(BaseModel):
    source: dict = Field(..., alias="_source")

    class Config:
        allow_population_by_field_name = True

request = ElasticsearchRequest(_source={'include': ['text']})

print(request.dict())
print(request.dict(by_alias=True))

Output:

{'source': {'include': ['text']}}
{'_source': {'include': ['text']}}

[rafa-acioly]

@StephenBrown2 how can i use the _id as non-required using alias? because the _id is only generated once have inserted a document on my collection, using your example we cannot instantiate a new class without the _id attribute.

[StephenBrown2]

Instead of using ... as the default, use None:

id: str = Field(None, alias="_id")