add union_mode='left_to_right' #7151
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davidhewitt
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Aug 16, 2023
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| To revert to the non-short-circuiting left-to-right behavior of V1, annotate the union with `Field(union_mode='left_to_right')`. | ||
| See [Union Mode](./usage/types/unions.md#union-mode) for more details. |
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I'm not an expert on V1's union validation, this statement may not be true. I thought it might be worth calling out this or something similar here in the migration guide.
dmontagu
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Aug 16, 2023
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@davidhewitt Thank you! This will greatly ease our transition to Pydantic V2! |
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Hi, just found this gem while migrating to V2. Is there a way to make this behavior as default..? |
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Change Summary
Adds a new
Fieldoption,union_mode, which can be used to alter the union validation. At present, there are only two options:smart(the default), which is equivalent to the current V2 behaviourleft_to_right, which is just simple left-to-right validation, first success wins, like V1This option can be used to opt out of smart union validation in cases when users want more easily understandable results.
In #7097 (comment) we suggested a
dumb_union=Trueboolean flag. In further discussion offline I raised the idea that using a string setting here (while a touch more verbose) is more descriptive and also gives us space to add more options backwards-compatibly later.Related issue number
Related #7097
Related #7110
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