avro - schema for logicalType - avro

Question

I am trying to learn avro and have a question in schema.
Some documents say
{
"name": "userid",
"type" : "string",
"logicalType" : "uuid"
},
And some say
{
"name": "userid",
"type" : {
"type" : "string",
"logicalType" : "uuid"
}
},
Which one is right? Or are they same?
Thank you!

Answer 1

I ran variants of your schemas with the avro tools "random" command ( aliased as avro below). It tries to generate a random value for a schema.
A schema with just this type using the nested type syntax to specify logicalType is rejected:
avro random --schema '{ "name": "userid", "type" : { "type": "string", "logicalType" : "uuid" } }' -
[...] No type: {"name":"userid","type":{"type":"string","logicalType":"uuid"}}
However, it works when putting the logicalType next to type:
avro random --schema ' { "type" : "string", "logicalType" : "uuid" }' -
[...] Objavro.schemaL{"type":"string","logicalType":"uuid"}avro.codecdeflate}�j�U�.�\�o���
Now, when we use it in a record, we get a warning when putting logicalType next to type:
avro random --schema '{ "type": "record", "fields": [ { "type" : "string", "logicalType" : "uuid", "name": "f"} ] , "name": "rec"}' -
[...] WARN avro.Schema: Ignored the rec.f.logicalType property ("uuid"). It should probably be nested inside the "type" for the field.
Objavro.schema�{"type":"record","name":"rec","fields":[{"name":"f","type":"string","logicalType":"uuid"}]}avro.codecdeflate��w�9�9�n�s�
The nested syntax is accepted without a warning:
avro random --schema '{ "type": "record", "fields": [ { "type" : { "type": "string", "logicalType" : "uuid" } , "name": "f"} ] , "name": "rec"}' -
�w<��qcord","name":"rec","fields":[{"name":"f","type":{"type":"string","logicalType":"uuid"}}]}avro.codecdeflate8��t
Further if we look at logicaltypes inside arrays:
avro random --count 1 --schema ' { "type": "array", "items": { "type" : "string", "logicalType" : "uuid" , "name": "f"} , "name": "farr" } ' -
[... random bits]
While the nested version fails:
avro random --count 1 --schema ' { "type": "array", "items": {"type": { "type" : "string", "logicalType" : "uuid" , "name": "f"} } , "name": "farr" } ' -
[...] No type: {"type":{"type":"string","logicalType":"uuid","name":"f"}}
It appears that if a logicalType is a type of a field in a record, you need to use the nested syntax.
Otherwise you need to use non-nested syntax.