Add pydantic v2 as output model type

[koxudaxi]

Related Issues: #803

Closes: #1255

from document

What is the difference between pydantic v1 and v2 output model?

Summary

datamodel-code-generator supports Pydantic v1 and v2 as output model type.

Pydantic v2 is a major release with many breaking changes. See the migration guide for more information:
https://docs.pydantic.dev/2.0/migration/

What's changes in v2 output?

__root__ field (a.k.a Custom Root Types)

__root__ field (a.k.a Custom Root Types) is removed in pydantic v2.
The model is changed to RootModel

pydantic.Field

https://docs.pydantic.dev/2.0/migration/#changes-to-pydanticfield

• const -> removed
• min_items (use min_length instead)
• max_items (use max_length instead)
• unique_items -> removed and the list type will be replaced by typing.Set. this feature is discussed in Add unique constraint to list? pydantic/pydantic-core#296
• allow_mutation (use frozen instead)
• regex (use pattern instead)

Model Config

• pydantic.Config -> pydantic.ConfigDict
• allow_mutation —> frozen (inverse value for getting same behavior).
• allow_population_by_field_name → populate_by_name

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (e9b6edf) 100.00% compared to head (5c82128) 100.00%.

Additional details and impacted files

@@             Coverage Diff             @@
##            master     #1391     +/-   ##
===========================================
  Coverage   100.00%   100.00%             
===========================================
  Files           11        32     +21     
  Lines         1020      3538   +2518     
  Branches       201       832    +631     
===========================================
+ Hits          1020      3538   +2518     

Flag	Coverage Δ
unittests	99.63% <99.57%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
datamodel_code_generator/__init__.py	100.00% <100.00%> (ø)
datamodel_code_generator/__main__.py	100.00% <100.00%> (ø)
datamodel_code_generator/format.py	100.00% <100.00%> (ø)
datamodel_code_generator/http.py	100.00% <100.00%> (ø)
datamodel_code_generator/imports.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/__init__.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/base.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/dataclass.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/enum.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/improts.py	100.00% <100.00%> (ø)
... and 22 more

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