postgres: (sub)select and combine optional content into an array - sql

Question

i have the following table structure:
Location----- * Media ----1 Attribute --------* AttributeTranslation
Each Location has n mediaitems attached, containing one optional attribute (text) and n associated translationa for that attribute.
I need to select this data into an array, so that i get for each location the associated medialist for each language.
what i currently do and what i get:
SELECT m.location_id, t.language_id,
array_agg_mult(
ARRAY[ARRAY[m.sortorder::text, m.filename, t.name]] ORDER BY m.sortorder
) as medialist
FROM Media m
LEFT JOIN ATTRIBUTE a ON a.id = m.attribute_id
LEFT JOIN AttributeTranslation t ON a.id = t.attribute_id
WHERE m.location_id = ?
GROUP BY m.location_id, t.language_id
This gives me following result for the given scenario: the current location has 4 images attached, only the first image has an associated attribute containing two translations:
Location_ID Language_ID MEDIALIST
AT_014 1 {{1,'location_image1.jpg','attribute german'}}
AT_014 2 {{1,'location_image1.jpg','attribute english'}}
AT_014 {{2,'location_image2.jpg',null},{3,'location_image3.jpg',null},{4,'location_image4.jpg',null}}
but what i need instead is this:
Location_ID Language_ID MEDIALIST
AT_014 1 {{1,'location_image1.jpg','attribute german'},{2,'location_image2.jpg',null},{3,'location_image3.jpg',null},{4,'location_image4.jpg',null}}
AT_014 2 {{1,'location_image1.jpg','attribute english'},{2,'location_image2.jpg',null},{3,'location_image3.jpg',null},{4,'location_image4.jpg',null}}
those 3 columns are part of a view, so that i can do later:
select * from locationview where location_id = ? and language_id = ?
how can i achieve the desired result here? thanks in advance!
Simplified Table Definitions:
CREATE TABLE LOCATION (
location_id numeric(20) primary key,
description text
);
CREATE TABLE MEDIA (
media_id numeric(20) primary key,
fileName text,
sortorder smallint,
location_id numeric(20) references LOCATION(location_id),
attribute_id numeric(20) references ATTRIBUTE(attribute_id)
);
CREATE TABLE ATTRIBUTE (
attribute_id numeric(20) primary key,
attributetype varchar(100),
);
CREATE TABLE ATTRIBUTETRANSLATION (
translation_id numeric(20),
language_id smallint,
name text,
description text,
attribute_id numeric(20) references ATTRIBUTE(attribute_id)
);
ALTER TABLE ATTRIBUTETRANSLATION add constraint AT_ID primary key(translation_id, language_id)

Answer 1

I am not sure I fully understand your question, but here's an attempt. You could take the output of your query, and match each row that has a language_id with the corresponding rows where language_id is NULL, so that you can then concatenate the medialist arrays. Here's a way to do that by creating an alias of your query with a CTE:
WITH t AS (
SELECT m.location_id, t.language_id,
array_agg(
ARRAY[ARRAY[m.sortorder::text, m.filename, t.name]] ORDER BY m.sortorder
) as medialist
FROM Media m
LEFT JOIN ATTRIBUTE a ON a.attribute_id = m.attribute_id
LEFT JOIN AttributeTranslation t ON a.attribute_id = t.attribute_id
WHERE m.location_id = ?
GROUP BY m.location_id, t.language_id
)
SELECT location_id, t1.language_id, t1.medialist || t2.medialist AS medialist
FROM (SELECT * FROM t WHERE language_id IS NOT NULL) t1
RIGHT OUTER JOIN (SELECT * FROM t WHERE language_id IS NULL) t2 USING (location_id);
I am not sure if this does exactly what you want, but hopefully it will give you some ideas.