Parameter binding using GQL in Google App Engine
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20-09-2019 - |
Question
Okay so I have this mode:
class Posts(db.Model):
rand1 = db.FloatProperty()
#other models here
and this controller:
class Random(webapp.RequestHandler):
def get(self):
rand2 = random.random()
posts_query = db.GqlQuery("SELECT * FROM Posts WHERE rand1 > :rand2 ORDER BY rand LIMIT 1")
#Assigning values for Django templating
template_values = {
'posts_query': posts_query,
#test purposes
'rand2': rand2,
}
path = os.path.join(os.path.dirname(__file__), 'templates/random.html')
self.response.out.write(template.render(path, template_values))
So when an entity is added a random float is generated (0-1) and then when I need to grab a random entity I want to be able to just use a simple SELECT query. It errors with:
BadArgumentError('Missing named arguments for bind, requires argument rand2',)
Now this works if I go:
posts_query = db.GqlQuery("SELECT * FROM Posts WHERE rand1 > 1 ORDER BY rand LIMIT 1")
So clearly my query is wrong; how does one use a variable in a where statement :S
Solution
Substitute:
"...WHERE rand1 > :rand2 ORDER BY rand LIMIT 1")
with:
"...WHERE rand1 > :rand2 ORDER BY rand LIMIT 1", rand2=rand2)
Or
"...WHERE rand1 > :1 ORDER BY rand LIMIT 1", rand2)
See for more information: "The Gql query class"
The funny thing is that I have just learned this about 2 hrs ago :P
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