Oracle: How to load hierachical JSON data into related tables - json

Question

I have got JSON data in a JSON column of an Oracle database. The JSON contains arrays and I should load the data into tables by means of PL/SQL. E. g.
{
"A1": "V1",
"A2": true,
"A3": 42,
"A4": [
{
"B1": "Q1",
"B4": [
{
"C1": "R1",
"C2": false
},
{
"C1": "R2",
"C2": false
}
]
},
{
"B1": "Q2",
"B4": [
{
"C1": "R3",
"C2": false
},
{
"C1": "R4",
"C2": true
}
]
}
]
}
{
"A1": "V2",
"A2": false,
"A3": 42,
"A4": [
{
"B1": "T1",
"B4": [
{
"C1": "S1",
"C2": false
},
{
"C1": "S2",
"C2": false
}
]
},
{
"B1": "T2",
"B4": [
{
"C1": "S3",
"C2": false
},
{
"C1": "S4",
"C2": true
}
]
}
]
}
The data should be loaded to three tables.
---
A
---
| 0..1
|
| 1..n
---
B (no (business) key available)
---
| 0..1
|
| 1..n
---
C
---
ID
A1
A2
A3
1
V1
true
42
2
V2
false
42
ID
ID A
B1
1
1
Q1
2
1
Q2
3
2
T1
4
2
T2
ID
ID B
C1
C2
1
1
R1
false
2
1
R2
false
3
1
R3
false
4
1
R4
true
5
2
S1
false
6
2
S2
false
7
2
S3
false
8
2
S4
true
I am trying to use JSON_TABLE to flatten the data for an implicit cursor of a for loop. I did so by using NESTED PATH. Now imagine we are in the for loop, i.e. for every "record" in C there is a record in the cursor/loop. While the data of C is "as is", the data of B gets mimeographed, and the data of A likewise, i.e.
A1
A2
A3
B1
C1
C2
V1
true
42
Q1
R1
false
V1
true
42
Q1
R2
false
V1
true
42
Q2
R3
false
V1
true
42
Q2
R4
true
V2
false
42
T1
S1
false
V2
false
42
T1
S2
false
V2
false
42
T2
S3
false
V2
false
42
T2
S4
true
My initial idea was to insert from the "A" data into table "A" only the first occurrence of a A-tuple saving the written ID by RETURNING .. INTO, insert the first occurrence of a B-tuple into "B" saving the written ID likewise and finally insert the C-tuple into "C". The problem here is to detect the change of the A-tuple respectively of the B-tuple. "A" should not be too much of a difficulty as it has a (business) key I also can preserve for checks. However, B has no (business) key.
My idea with B was to use an unknown, maybe inexistent pseudo column JSON_TABLE/NESTED PATH provides, that tells e.g. to which expression of "B" the current "C" belongs to. In fact, it would be a key for "B". Yet, I have not found anything in the Oracle docs and on the internet. Do you happen to know such a column?
As an alternative, I think about not using the NESTED PATH for "C" but return the array as JSON column and afterwards to somehow create an inner for loop, but I do not know how to use a JSON typed PL/SQL variable to extract an array of objects as nested table of some sort to be able to use as for loop cursor. Do you happen to know examples for such?
Is there a way, I miss completely?
Kind regards
Thiemo