Hello Bryś Andrzej,
Greetings! Welcome to Microsoft Q&A Platform.
I understand that you’re having trouble with your Azure Blob Storage indexer not reading metadata correctly and from the issue description, you are getting null values for the custom metadata fields that you wanted to transition to the Search Index as retrievable fields. You also tried to add the field mapping to the indexer, but still the metadata was not copied to the index, but the new field is always null. kindly check the logs to fetch more details about the error: Diagnostic settings.
Troubleshooting common indexer errors and warnings in Azure AI Search
In Azure AI Search a vectorizer is software that performs vectorization, such as a deployed embedding model on Azure OpenAI, that converts text (or images) to vectors during query execution.
It's defined in a search index, it applies to searchable vector fields, and it's used at query time to generate an embedding for a text or image query input. If instead you need to vectorize content as part of the indexing process, refer to Integrated Vectorization (Preview). For built-in vectorization during indexing, you can configure an indexer and skillset that calls an embedding model for your raw text content.
refer - https://learn.microsoft.com/en-us/azure/search/vector-search-how-to-configure-vectorizer,
https://learn.microsoft.com/en-us/azure/architecture/ai-ml/architecture/search-blob-metadata
Ensure that the indexer has the necessary read permissions for the blob storage. The managed identity of the search service should have Storage Blob Data Reader permissions. Ensure that the data source configuration is correct and that the blobs contain the “Project” metadata. You can manually inspect a few blobs to confirm that the metadata is present and correctly formatted. Check the indexer logs for any errors or warnings that might indicate why the “Project” field is not being populated. The logs can provide detailed information about any issues encountered during the indexing process.
refer - https://learn.microsoft.com/en-us/azure/search/search-howto-indexing-azure-blob-storage,https://learn.microsoft.com/en-us/azure/search/search-howto-index-one-to-many-blobs,https://github.com/Azure/azure-search-vector-samples/issues/71.
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