How to index objects inside array in JSONB field?

Question

I want to index the JSONB field with GIN indexing. Inside this field, I have an array of objects . Precisely, this is how it looks (shortened second object with three dots):

[
    {
        "tags": ["student work", "fast apply"],
        "intensity": [
            {
                "shift": "fulltime",
                "period": "hours",
                "duration": "9"
            },
            {
                "shift": "parttime",
                "period": "hours",
                "duration": "4"
            }
        ]
    },
    { ... }
]

This is how I filter this table in WHERE clause:

items.intensity @? '$[*] ? (@.tags == "student work" || @.tags == "undefined" || @.tags.size() == 0) ? (@.intensity[*].shift == "fulltime")'

This is the index I tried but didn't work:

CREATE INDEX idxginintensitytags ON items USING GIN (intensity jsonb_path_ops);

Explain analyze:

    #   Node    Rows    Loops
Actual
1.  Bitmap Heap Scan on items as items (rows=154922 loops=1)
Recheck Cond: (intensity @? '$[*]?(@."intensity"[*]."shift" == "fulltime")'::jsonpath)
Heap Blocks: exact=33478
154922  1
2.  Bitmap Index Scan using idxginintensitytags (rows=154922 loops=1)
Index Cond: (intensity @? '$[*]?(@."intensity"[*]."shift" == "fulltime")'::jsonpath)
154922  1

I want to filter my table by tags , shifts , periods , and durations . I have 200,000 rows in that table .

How can I index this field ?

I am using the latest version - PostgreSQL 13 .

Answer 1

In my hands, a problem is that it does use the index, even though doing so is slower. And the reason for that is that @.tags.size() == 0 cannot be determined by the index, so it ends ups returning all table rows to be rechecked, but the planner evidently doesn't realize this will happen.

Can you express this concept in a different way?