Postgres JSONB Query and Index on Nested String Array - arrays

Question

I have some troubles wrapping my head around how to formulate queries and provide proper indices for the following situation. I have customer entities represented in JSON like this (only relevant properties are retained):
{
"id": "50000",
"address": [
{
"line": [
"2nd Main Street",
"123 Harris Plaza"
],
"city": "Boston",
"state": "Massachusetts",
"country": "US",
},
{
"line": [
"1st Av."
],
"city": "Jamestown",
"state": "Massachusetts",
"country": "US",
}
]
}
The customers are stored in the following customer table:
CREATE TABLE Customer (
id BIGSERIAL PRIMARY KEY,
resource JSONB
);
I manage to do simple queries on the resource column, e.g. a projection query like this works (retrieve all lower-case address lines for cities starting with "bo"):
SELECT LOWER(jsonb_array_elements_text(jsonb_array_elements(c.resource#>'{address}') #> '{line}')) FROM Customer c, jsonb_array_elements(c.resource #> '{address}') a WHERE LOWER(a->>'city') LIKE 'bo%';
I have trouble doing the following: my goal is to query all customers that have at least one address line beginning with "12". Case insensitivity is a requirement for my use case. The example customer would match my query, as the first address object has an address line starting with "12". Please note that "line" is an Array of JSON Strings, not complex objects. So far the closest thing I could come up with is this:
SELECT c.resource FROM Customer c, jsonb_array_elements(c.resource #> '{address}') a WHERE a->'line' ?| array['123 Harris Plaza'];
Obviously this is not a case-insensitive LIKE query. Any help/pointers on how to formulate both query and accompanying GIN index are greatly appreciated. My first query already selects all address lines as text, so maybe this could be used in a GIN index?
I'm using Postres 9.5, but am happy to upgrade if this can only be achieved in more recent Postgres versions.

Answer 1

While GIN indexes have machinery to support prefix matching, this machinery is only hooked up for tsvectors. array_ops does not have it hooked up, nor does json_ops or json_path_ops. So unless you want to create new operator class/families (or normalize your data into separate tables) you will have to shoe-horn your data into a tsvector.
Here is a crude way to do that, which doesn't account for the possibility that a address line might contain literal single quotes or perhaps other meaningful characters:
create function addressline_tsvector(jsonb) returns tsvector immutable language SQL as $$
select string_agg('''' || lower(value) || '''', ' ')::tsvector
from jsonb_array_elements($1->'address') a(a),
jsonb_array_elements_text(a->'line')
$$;
create index on customer using gin (addressline_tsvector(resource));
select * from customer where addressline_tsvector(resource) ## lower('''2nd Main'':*')::tsquery;
Given that your example table only has one row, the index will probably not actually be used unless you set enable_seqscan = off first.