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fastavro gives a default value for unions with nulls that don't have a default value #49

movermeyer opened this issue May 19, 2016 · 4 comments


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@movermeyer movermeyer commented May 19, 2016

This is somewhat related to #48. Given this example schema:

protocol test {
  record a {
    int x;
    union {null, int} y;

the following should fail:

>>> data = StringIO.StringIO()
>>> fastavro.writer(data, schema, [{'val': {'x': 1}}])

However, it does not, giving a default value of null to a field ('y') without a default value.

This stems from the use of .get(), which returns None if the key is not found.
The field does not have a default value, so datum.get('default') returns None, which is then used as the default value.

This is just mixing up the lack of a value, with a value of null. Instead, the code should check for the field's existence in the datum, and return false if it doesn't exist.

This is related to #37, in that having write_record call validate() on itself would catch this. Although I imagine the overhead might raise some ire, so there are some options.

Some pull requests will be made in a bit.

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@movermeyer movermeyer commented May 19, 2016

In general, this is a problem with not checking to make sure that the datum contains a value for each field or the field has a default.

In this specific case, it results in data being made up.

movermeyer pushed a commit to movermeyer/fastavro that referenced this issue May 19, 2016
Have the record validate itself before writing out.
e-heller added a commit to e-heller/fastavro that referenced this issue May 22, 2016
Create a `NoValue` sentinel object for this case. Previously, `None`
would be deduced, but Python's `None` is conflated with the Avro type
`null` and can causes issues with `union` records that contain a `null`
type. See fastavro#49
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@movermeyer movermeyer commented May 24, 2016

I like @e-heller's solution better. Solves this problem and shouldn't have noticeable impact on performance.

e-heller added a commit to e-heller/fastavro that referenced this issue May 27, 2016
For any `x = object()`, `bool(x) == True`. However we do not want the
special `NoValue` sentinel to be mistaken as any valid type. Implement
a `__bool__` method on the `_NoValue` class to raise a TypeError.
See: fastavro#49
tebeka added a commit that referenced this issue Jun 6, 2016
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@tebeka tebeka commented Jun 12, 2016

0.9.10 should fix this

@tebeka tebeka closed this Jun 12, 2016
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@movermeyer movermeyer commented Jun 12, 2016

Looks good. Thanks.

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