How to map a json string into object type in sink transformation - azure-data-factory

Question

Using Azure Data Factory and a data transformation flow. I have a csv that contains a column with a json object string, below an example including the header:
"Id","Name","Timestamp","Value","Metadata"
"99c9347ab7c34733a4fe0623e1496ffd","data1","2021-03-18 05:53:00.0000000","0","{""unit"":""%""}"
"99c9347ab7c34733a4fe0623e1496ffd","data1","2021-03-19 05:53:00.0000000","4","{""jobName"":""RecipeB""}"
"99c9347ab7c34733a4fe0623e1496ffd","data1","2021-03-16 02:12:30.0000000","state","{""jobEndState"":""negative""}"
"99c9347ab7c34733a4fe0623e1496ffd","data1","2021-03-19 06:33:00.0000000","23","{""unit"":""kg""}"
Want to store the data in a json like this:
{
"id": "99c9347ab7c34733a4fe0623e1496ffd",
"name": "data1",
"values": [
{
"timestamp": "2021-03-18 05:53:00.0000000",
"value": "0",
"metadata": {
"unit": "%"
}
},
{
"timestamp": "2021-03-19 05:53:00.0000000",
"value": "4",
"metadata": {
"jobName": "RecipeB"
}
}
....
]
}
The challenge is that metadata has dynamic content, meaning, that it will be always a json object but the content can vary. Therefore I cannot define a schema. Currently the column "metadata" on the sink schema is defined as object, but whenever I run the transformation I run into an exception:
Conversion from ArrayType(StructType(StructField(timestamp,StringType,false),
StructField(value,StringType,false), StructField(metadata,StringType,false)),true) to ArrayType(StructType(StructField(timestamp,StringType,true),
StructField(value,StringType,true), StructField(metadata,StructType(StructField(,StringType,true)),true)),false) not defined

Answer 1

We can get the output you expected, we need the expression to get the object Metadata.value.
Please ref my steps, here's my source:
Derived column expressions, create a JSON schema to convert the data:
#(id=Id,
name=Name,
values=#(timestamp=Timestamp,
value=Value,
metadata=#(unit=substring(split(Metadata,':')[2], 3, length(split(Metadata,':')[2])-6))))
Sink mapping and output data preview:
The key is that your matadata value is an object and may have different schema and content, may be 'value' or other key. We only can manually build the schema, it doesn't support expression. That's the limit.
We can't achieve that within Data Factory.
HTH.