How Can I Successfully Scan Nested Structs Using SQLx?

Nested Struct Scanning with SQLx

When attempting to scan query results into nested structs with SQLx, users may encounter errors such as missing destination names. This issue arises when the struct field names and database column names do not exactly match.

Solution: Embedding Nested Structs

As suggested in the SQLx documentation, the correct approach is to embed the nested structs within the parent struct. For instance:

In this example, the Address struct is embedded within the Customer struct. By embedding the nested struct, the field names and tags associated with Address are promoted into Customer. Consequently, SQLx can correctly map the results to the appropriate fields.

Avoid Field Duplication

It's important to note that embedding the nested struct will also result in the flattening of the output during JSON marshalling. To maintain the original nested structure, you can remap the database struct to the original type. Alternatively, you could scan the query result into a map[string]interface{}, but this requires careful handling of Postgres data types in Go.

Conclusion

Following these guidelines ensures correct scanning of results into nested structs using SQLx. By properly embedding the nested structs or utilizing alternative approaches like remapping or scanning into a map, you can effectively extract complex data structures from your database.

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