entity already exists - but it does not

I've not seen an issue like this before. Is "entity already exists" the exact error message?

If you enable the Feeds Log module, does that reveal more information? With that module, after an import, you can see the exact data that Feeds receives and how the data looked like after parsing. Or did you already try that and is that where you got the "entity already exists" message from?

Are the ID's of the two nodes 1904 and 1905? In the column "Entität" I see that are the node ID's that Feeds found when looking for existing entities (I see it only reports the ID instead of a link to the entity, probably because of avoiding loading the whole node).

The most likely cause is a misconfiguration on the mapping settings. Which target(s) do you have marked as unique? Have you perhaps set more than one target as unique? Feeds loops through all targets set as unique and tries to find an existing entity based on each individually. It does not look for existing entities based on a combination of targets. That behavior is perhaps a bit confusing. I'm not sure if that behavior was intentionally or not (it already worked that way before I took over the development of Feeds).

Alright, can you share your feed type configuration + a sample source file with which the issue can be reproduced?

Okay, that is strange. When I add mapping to a field that cannot be marked as unique, I don't get the "unique" key set. And for mappings where "unique" is not checked, I get "unique" => []. So I wonder how something like "unique" => ["value"=> 0] could happen.

That being said, your fix seems reasonable. Just want to know if there is perhaps another bug in the UI that got you to this unusual state.

Can you share your feed type configuration as well? (yml file) Maybe that helps to discover a bug in the UI as well.

What you mean with "When I add mapping to a field that cannot be marked as unique"?

When I have the following mapping configuration:

I get:

mappings:
  -
    target: title
    map:
      value: ''
    settings:
      language: null
    unique: {  }
  -
    target: field_date
    map:
      value: ''
    settings:
      language: null
      timezone: UTC

And with the following:

I get:

mappings:
  -
    target: title
    map:
      value: ''
    settings:
      language: null
    unique:
      value: 1
  -
    target: field_date
    map:
      value: ''
    settings:
      language: null
      timezone: UTC

I never get:

    unique:
      value: '0'

Like you got.

It is still however worth it to add a fix for when "unique" has a value of zero. I just don't know how that could happen. There is a chance that there is another bug, probably in the UI, that is causing it.

I've added a test and a possible fix for the issue.

I've slightly changed the fix, because I think it is unnecessary to check the unique flags on mappings every time getMappings() gets called - also because I think it's very uncommon to occur (only happens when manually editing the config file). But resaving the feed type would be enough for the fix to have effect.

I've scheduled merging the code!