My JSON in the db is like this:
{
"ingredients": [
"3 tablespoons almond butter",
...
"Lime wedges"
],
"instructions": [
"In a bowl"
]
"tags": [
"gluten-free",
"grain bowls",
"Thai"
]
}
My app.py file:
class Recipe(db.Model):
__tablename__ = "recipe"
....
recipe = db.Column(db.JSON)
I'm trying, for starters, to select all records with the "Thai" tag.
Recipe.query.filter(Recipe.recipe['tags'].contains(["Thai"])).all()
tells me I might need explicit type casts, I've tried astext and cast.. nothing seems to be working. Not sure what I'm doing wrong.
here's the end of the stack trace:
sqlalchemy.exc.ProgrammingError: (psycopg2.errors.UndefinedFunction) operator does not exist: json ~~ text
LINE 3: WHERE ((recipe.recipe -> 'tags') LIKE '%' || CAST('["%Thai%"...
^
HINT: No operator matches the given name and argument types. You might need to add explicit type casts.
[SQL: SELECT recipe.id AS recipe_id, recipe.url_id AS recipe_url_id, recipe.author AS recipe_author, recipe.description AS recipe_description, recipe.recipe AS recipe_recipe
FROM recipe
WHERE ((recipe.recipe -> %(recipe_1)s) LIKE '%%' || CAST(%(param_1)s AS JSON) || '%%')]
[parameters: {'recipe_1': 'tags', 'param_1': '["%Thai%"]'}]
With that I tried:
Recipe.query.filter(Recipe.recipe['tags'].contains(cast(["%Thai%"], JSON)))
What has worked is
db.engine.execute(text("select * from recipe where recipe->> 'tags' like '%Thai%'"))
I can live with that but am stubbornly wanting it to happen thru the ORM.
The only clue I have is that in the stack trace I'm seeing it generates a sql statement with -> not ->> ... but I can't figure how to get the ->>
Then I found this:
tags_subquery = db.session.query(func.json_array_elements(Recipe.recipe['tags']).label('tags')).subquery()
query = db.session.query(Recipe, tags_subquery.c.tags).filter(tags_subquery.c.tags.op('->>')('tags').like("%Thai%"))
And there's no error, but an empty result... I think I'm somewhat close now thanks to @r-m-n
CodePudding user response:
You can avoid the error by casting the left hand side of the expression to a text type:
# select cast('{"a": ["spam", "ham"]}'::json->'a' as text) like '%spam%' as "Exists?";
Exists?
═════════
t
but this will also match substrings, which may not be desirable:
# select cast('{"a": ["spam", "ham"]}'::json->'a' as text) like '%am%' as "Exists?";
Exists?
═════════
t
A better option would be to cast to jsonb:
# select cast('{"a": ["spam", "ham"]}'::json->'a' as jsonb) @> '["spam"]' as "Exists?";
Exists?
═════════
t
# select cast('{"a": ["spam", "ham"]}'::json->'a' as jsonb) @> '["am"]' as "Exists?";
Exists?
═════════
f
On the Python side, this would look like
from sqlalchemy import cast
from sqlalchemy.dialects.postgresql import JSONB
result = Recipe.query.filter(
cast(Recipe.recipe['tags'], JSONB).contains(["Thai"])
).all()
Changing the column type to JSONB would remove the need for casting (but would require a migration):
class Recipe(db.Model)
...
recipe = sb.Column(JSONB)
result = Recipe.filter(Recipe.recipe['tags'].contains(['Thai'])).all()
You can see how JSON(B) comparison methods map to Postgresql functions in the source.