I want to write a query that does something like this SQL query:
SELECT name FROM contacts WHERE blah blah
I know I can do something like this:
for contact in Contacts.gql(WHERE_CLAUSE, args).fetch(1000):
print contact.name
but isn't there a way to get name directly from a query without having to loop on the results? would it provide any advantage in performance?
Nope. Can't be done.
A GQL query returns zero or more entities or Keys of the requested
kind. Every GQL query always begins with either SELECT * or SELECT
key. (A GQL query cannot perform a SQL-like "join" query.)
http://code.google.com/appengine/docs/python/datastore/gqlreference.html
But you can create a simple wrapper to do it for you. Something like:
def get_all_of_field(model, field):
for x in model.all():
yield getattr(x, field)
names = get_all_of_field(Contact, 'name')
Performance can't be improved that way as the entire "line" is read by the API no matter what. Either you read the entire "line" or just its key.
You can do this now using Projection queries. For db, see the documentation here:
https://developers.google.com/appengine/docs/python/datastore/projectionqueries
For ndb, see the documentation here:
https://developers.google.com/appengine/docs/python/ndb/queries#projection
Related
I have a situation where I have to search a document in Solr with multiple OR keywords. Now the number of keywords may lead up to 5000 which is resulting in a awfully large query with 5000 OR conditions. This is resulting in the Solr server to hang. Is there any other way I can design the query to work. Short sample of the query is given below
tweet_id:337931022601699328 OR 337931064293081089 OR 337931089538584576 OR 337931098761871361 OR 337931138851016704 OR 337931143099854848 OR 337931160082591745 OR 337931163857453056 OR 337931230819516416 OR 337931239996665857 OR 337931287518126080 OR 337931322850951168 OR 337931325648535553 OR 337931331398934528 OR 337931413057830912 OR 337931442363441152 OR 337931448629731329 OR 337931453344129025 OR 337931465016877056 OR 337931482066726912 OR 337931514388029442 OR 337931533149155328 OR 337931645527130114 OR 337931704935256064 OR 337931784459268096 OR 337931845545103360 OR 337931889086185472 OR 337931892668108801 OR 337931963983855617 OR 337932154212319233 OR 337932176454721536 OR 337932193198374912 OR 337932229659459584 OR 337932437290090496 OR 337932436807749632 OR 337932436828725250 OR 337932437449474048 OR 337932448518250496 OR 337932458832035843 OR 337932458634915840 OR 337932458278387712 OR 337932474246119425 OR 337932476209041409 OR 337932477408620544 OR 337932480478842880 OR 337932478775959554 OR 337932480566931456 OR 337932478763376640 OR 337932481841999872 OR 337932479337992192 OR 337932479296045057 OR 337932479333797889 OR 337932484614434816 OR 337932484606038017 OR 337932482777317376 OR 337932484664758272 OR 337932482785718273 OR 337932484589273088 OR 337932487399444481 OR 337932489031032833 OR 337932489114923008 OR 337932486573166592 OR 337932490704560130 OR 337932489144270848 OR 337932488762601472 OR 337932492097069056 OR 337932497780355072 OR 337932498900230144 OR 337932499722321921 OR 337932514431729665 OR 337932561806409731 OR 337932567284154368 OR 337932567300935680 OR 337932574603214848 OR 337932571134533632 OR 337932574674518016 OR 337932575484026881 OR 337932578206121984 OR 337932582215892994 OR 337932586653454336 OR 337932584917024768 OR 337932592986865664 OR 337932597017587712 ....
I intend to facet the result based on a few fields.
I'm not sure whether this solution would help you or not, but tried something for your problem.
Whatever the query you provide to Solr, first it parses that query to it's understandable format. Then Solr executes that for result. You have to do some calculations before querying to Solr. Let's take the following scenario to solve your use case.
Suppose You have total 5000 tweet_id. You have to do an OR query on around 4000 tweet_id. In this type of scenario, it's better to query on other (5000-4000=1000) 1000 tweet_id with negation AND query. So, your query will have less values passed.
So, try querying with rest of the tweet_id with negation AND query instead of OR query.
If I were you, I'd create a new field denoting this custom_list_id .. Whenever you generate a new list, index the new data then query by the list I'd.
Select all records, ID which is not in the list
How to make like :
query = Story.all()
query.filter('ID **NOT IN** =', [100,200,..,..])
There's no way to do this efficiently in App Engine. You should simply select everything without that filter, and filter out any matching entities in your code.
This is now supported via GQL query
The 'IN' and '!=' operators in the Python runtime are actually
implemented in the SDK and translate to multiple queries 'under the
hood'.
For example, the query "SELECT * FROM People WHERE name IN ('Bob',
'Jane')" gets translated into two queries, equivalent to running
"SELECT * FROM People WHERE name = 'Bob'" and "SELECT * FROM People
WHERE name = 'Jane'" and merging the results. Combining multiple
disjunctions multiplies the number of queries needed, so the query
"SELECT * FROM People WHERE name IN ('Bob', 'Jane') AND age != 25"
generates a total of four queries, for each of the possible conditions
(age less than or greater than 25, and name is 'Bob' or 'Jane'), then
merges them together into a single result set.
source: appengine blog
This is an old question, so I'm not sure if the ID is a non-key property. But in order to answer this:
query = Story.all()
query.filter('ID **NOT IN** =', [100,200,..,..])
...With ndb models, you can definitely query for items that are in a list. For example, see the docs here for IN and !=. Here's how to filter as the OP requested:
query = Story.filter(Story.id.IN([100,200,..,..])
We can even query for items that in a list of repeated keys:
def all(user_id):
# See if my user_id is associated with any Group.
groups_belonged_to = Group.query().filter(user_id == Group.members)
print [group.to_dict() for group in belong_to]
Some caveats:
There's docs out there that mention that in order to perform these types of queries, Datastore performs multiple queries behind the scenes, which (1) might take a while to execute, (2) take longer if you searching in repeated properties, and (3) will up your costs with more operations.
Simple one really. In SQL, if I want to search a text field for a couple of characters, I can do:
SELECT blah FROM blah WHERE blah LIKE '%text%'
The documentation for App Engine makes no mention of how to achieve this, but surely it's a common enough problem?
BigTable, which is the database back end for App Engine, will scale to millions of records. Due to this, App Engine will not allow you to do any query that will result in a table scan, as performance would be dreadful for a well populated table.
In other words, every query must use an index. This is why you can only do =, > and < queries. (In fact you can also do != but the API does this using a a combination of > and < queries.) This is also why the development environment monitors all the queries you do and automatically adds any missing indexes to your index.yaml file.
There is no way to index for a LIKE query so it's simply not available.
Have a watch of this Google IO session for a much better and more detailed explanation of this.
i'm facing the same problem, but i found something on google app engine pages:
Tip: Query filters do not have an explicit way to match just part of a string value, but you can fake a prefix match using inequality filters:
db.GqlQuery("SELECT * FROM MyModel WHERE prop >= :1 AND prop < :2",
"abc",
u"abc" + u"\ufffd")
This matches every MyModel entity with a string property prop that begins with the characters abc. The unicode string u"\ufffd" represents the largest possible Unicode character. When the property values are sorted in an index, the values that fall in this range are all of the values that begin with the given prefix.
http://code.google.com/appengine/docs/python/datastore/queriesandindexes.html
maybe this could do the trick ;)
Altough App Engine does not support LIKE queries, have a look at the properties ListProperty and StringListProperty. When an equality test is done on these properties, the test will actually be applied on all list members, e.g., list_property = value tests if the value appears anywhere in the list.
Sometimes this feature might be used as a workaround to the lack of LIKE queries. For instance, it makes it possible to do simple text search, as described on this post.
You need to use search service to perform full text search queries similar to SQL LIKE.
Gaelyk provides domain specific language to perform more user friendly search queries. For example following snippet will find first ten books sorted from the latest ones with title containing fern
and the genre exactly matching thriller:
def documents = search.search {
select all from books
sort desc by published, SearchApiLimits.MINIMUM_DATE_VALUE
where title =~ 'fern'
and genre = 'thriller'
limit 10
}
Like is written as Groovy's match operator =~.
It supports functions such as distance(geopoint(lat, lon), location) as well.
App engine launched a general-purpose full text search service in version 1.7.0 that supports the datastore.
Details in the announcement.
More information on how to use this: https://cloud.google.com/appengine/training/fts_intro/lesson2
Have a look at Objectify here , it is like a Datastore access API. There is a FAQ with this question specifically, here is the answer
How do I do a like query (LIKE "foo%")
You can do something like a startWith, or endWith if you reverse the order when stored and searched. You do a range query with the starting value you want, and a value just above the one you want.
String start = "foo";
... = ofy.query(MyEntity.class).filter("field >=", start).filter("field <", start + "\uFFFD");
Just follow here:
init.py#354">http://code.google.com/p/googleappengine/source/browse/trunk/python/google/appengine/ext/search/init.py#354
It works!
class Article(search.SearchableModel):
text = db.TextProperty()
...
article = Article(text=...)
article.save()
To search the full text index, use the SearchableModel.all() method to get an
instance of SearchableModel.Query, which subclasses db.Query. Use its search()
method to provide a search query, in addition to any other filters or sort
orders, e.g.:
query = article.all().search('a search query').filter(...).order(...)
I tested this with GAE Datastore low-level Java API. Me and works perfectly
Query q = new Query(Directorio.class.getSimpleName());
Filter filterNombreGreater = new FilterPredicate("nombre", FilterOperator.GREATER_THAN_OR_EQUAL, query);
Filter filterNombreLess = new FilterPredicate("nombre", FilterOperator.LESS_THAN, query+"\uFFFD");
Filter filterNombre = CompositeFilterOperator.and(filterNombreGreater, filterNombreLess);
q.setFilter(filter);
In general, even though this is an old post, a way to produce a 'LIKE' or 'ILIKE' is to gather all results from a '>=' query, then loop results in python (or Java) for elements containing what you're looking for.
Let's say you want to filter users given a q='luigi'
users = []
qry = self.user_model.query(ndb.OR(self.user_model.name >= q.lower(),self.user_model.email >= q.lower(),self.user_model.username >= q.lower()))
for _qry in qry:
if q.lower() in _qry.name.lower() or q.lower() in _qry.email.lower() or q.lower() in _qry.username.lower():
users.append(_qry)
It is not possible to do a LIKE search on datastore app engine, how ever creating an Arraylist would do the trick if you need to search a word in a string.
#Index
public ArrayList<String> searchName;
and then to search in the index using objectify.
List<Profiles> list1 = ofy().load().type(Profiles.class).filter("searchName =",search).list();
and this will give you a list with all the items that contain the world you did on the search
If the LIKE '%text%' always compares to a word or a few (think permutations) and your data changes slowly (slowly means that it's not prohibitively expensive - both price-wise and performance-wise - to create and updates indexes) then Relation Index Entity (RIE) may be the answer.
Yes, you will have to build additional datastore entity and populate it appropriately. Yes, there are some constraints that you will have to play around (one is 5000 limit on the length of list property in GAE datastore). But the resulting searches are lightning fast.
For details see my RIE with Java and Ojbectify and RIE with Python posts.
"Like" is often uses as a poor-man's substitute for text search. For text search, it is possible to use Whoosh-AppEngine.
I have a basic "property bag" table that stores attributes about my primary table "Card." So when I want to start doing some advanced searching for cards, I can do something like this:
SELECT dbo.Card.Id, dbo.Card.Name
FROM dbo.Card
INNER JOIN dbo.CardProperty ON dbo.CardProperty.IdCrd = dbo.Card.Id
WHERE dbo.CardProperty.IdPrp = 3 AND dbo.CardProperty.Value = 'Fiend'
INTERSECT
SELECT dbo.Card.Id, dbo.Card.Name
FROM dbo.Card
INNER JOIN dbo.CardProperty ON dbo.CardProperty.IdCrd = dbo.Card.Id
WHERE (dbo.CardProperty.IdPrp = 10 AND (dbo.CardProperty.Value = 'Wind' OR dbo.CardProperty.Value = 'Fire'))
What I need to do is to extract this idea into some kind of stored procedure, so that ideally I can pass in a list of property/value combinations and get the results of the search.
Initially this is going to be a "strict" search meaning that the results must match all elements in the query, but I'd also like to have a "loose" query so that it would match any of the results in the query.
I can't quite seem to wrap my head around this one. My previous version of this was to do generate some massive SQL query to execute with a lot of AND/OR clauses in it, but I'm hoping to do something a little more elegant this time. How do I go about doing this?
it seems to me that you have an EAV model here.
if you're using sql server 2005 and up i'd suggest you use XML datatype for this:
http://weblogs.sqlteam.com/mladenp/archive/2006/10/14/14032.aspx
makes searching and stuff much easier with built in xml querying capabilities.
if you can't change your model then look at this:
http://weblogs.sqlteam.com/davidm/articles/12117.aspx
Simple one really. In SQL, if I want to search a text field for a couple of characters, I can do:
SELECT blah FROM blah WHERE blah LIKE '%text%'
The documentation for App Engine makes no mention of how to achieve this, but surely it's a common enough problem?
BigTable, which is the database back end for App Engine, will scale to millions of records. Due to this, App Engine will not allow you to do any query that will result in a table scan, as performance would be dreadful for a well populated table.
In other words, every query must use an index. This is why you can only do =, > and < queries. (In fact you can also do != but the API does this using a a combination of > and < queries.) This is also why the development environment monitors all the queries you do and automatically adds any missing indexes to your index.yaml file.
There is no way to index for a LIKE query so it's simply not available.
Have a watch of this Google IO session for a much better and more detailed explanation of this.
i'm facing the same problem, but i found something on google app engine pages:
Tip: Query filters do not have an explicit way to match just part of a string value, but you can fake a prefix match using inequality filters:
db.GqlQuery("SELECT * FROM MyModel WHERE prop >= :1 AND prop < :2",
"abc",
u"abc" + u"\ufffd")
This matches every MyModel entity with a string property prop that begins with the characters abc. The unicode string u"\ufffd" represents the largest possible Unicode character. When the property values are sorted in an index, the values that fall in this range are all of the values that begin with the given prefix.
http://code.google.com/appengine/docs/python/datastore/queriesandindexes.html
maybe this could do the trick ;)
Altough App Engine does not support LIKE queries, have a look at the properties ListProperty and StringListProperty. When an equality test is done on these properties, the test will actually be applied on all list members, e.g., list_property = value tests if the value appears anywhere in the list.
Sometimes this feature might be used as a workaround to the lack of LIKE queries. For instance, it makes it possible to do simple text search, as described on this post.
You need to use search service to perform full text search queries similar to SQL LIKE.
Gaelyk provides domain specific language to perform more user friendly search queries. For example following snippet will find first ten books sorted from the latest ones with title containing fern
and the genre exactly matching thriller:
def documents = search.search {
select all from books
sort desc by published, SearchApiLimits.MINIMUM_DATE_VALUE
where title =~ 'fern'
and genre = 'thriller'
limit 10
}
Like is written as Groovy's match operator =~.
It supports functions such as distance(geopoint(lat, lon), location) as well.
App engine launched a general-purpose full text search service in version 1.7.0 that supports the datastore.
Details in the announcement.
More information on how to use this: https://cloud.google.com/appengine/training/fts_intro/lesson2
Have a look at Objectify here , it is like a Datastore access API. There is a FAQ with this question specifically, here is the answer
How do I do a like query (LIKE "foo%")
You can do something like a startWith, or endWith if you reverse the order when stored and searched. You do a range query with the starting value you want, and a value just above the one you want.
String start = "foo";
... = ofy.query(MyEntity.class).filter("field >=", start).filter("field <", start + "\uFFFD");
Just follow here:
init.py#354">http://code.google.com/p/googleappengine/source/browse/trunk/python/google/appengine/ext/search/init.py#354
It works!
class Article(search.SearchableModel):
text = db.TextProperty()
...
article = Article(text=...)
article.save()
To search the full text index, use the SearchableModel.all() method to get an
instance of SearchableModel.Query, which subclasses db.Query. Use its search()
method to provide a search query, in addition to any other filters or sort
orders, e.g.:
query = article.all().search('a search query').filter(...).order(...)
I tested this with GAE Datastore low-level Java API. Me and works perfectly
Query q = new Query(Directorio.class.getSimpleName());
Filter filterNombreGreater = new FilterPredicate("nombre", FilterOperator.GREATER_THAN_OR_EQUAL, query);
Filter filterNombreLess = new FilterPredicate("nombre", FilterOperator.LESS_THAN, query+"\uFFFD");
Filter filterNombre = CompositeFilterOperator.and(filterNombreGreater, filterNombreLess);
q.setFilter(filter);
In general, even though this is an old post, a way to produce a 'LIKE' or 'ILIKE' is to gather all results from a '>=' query, then loop results in python (or Java) for elements containing what you're looking for.
Let's say you want to filter users given a q='luigi'
users = []
qry = self.user_model.query(ndb.OR(self.user_model.name >= q.lower(),self.user_model.email >= q.lower(),self.user_model.username >= q.lower()))
for _qry in qry:
if q.lower() in _qry.name.lower() or q.lower() in _qry.email.lower() or q.lower() in _qry.username.lower():
users.append(_qry)
It is not possible to do a LIKE search on datastore app engine, how ever creating an Arraylist would do the trick if you need to search a word in a string.
#Index
public ArrayList<String> searchName;
and then to search in the index using objectify.
List<Profiles> list1 = ofy().load().type(Profiles.class).filter("searchName =",search).list();
and this will give you a list with all the items that contain the world you did on the search
If the LIKE '%text%' always compares to a word or a few (think permutations) and your data changes slowly (slowly means that it's not prohibitively expensive - both price-wise and performance-wise - to create and updates indexes) then Relation Index Entity (RIE) may be the answer.
Yes, you will have to build additional datastore entity and populate it appropriately. Yes, there are some constraints that you will have to play around (one is 5000 limit on the length of list property in GAE datastore). But the resulting searches are lightning fast.
For details see my RIE with Java and Ojbectify and RIE with Python posts.
"Like" is often uses as a poor-man's substitute for text search. For text search, it is possible to use Whoosh-AppEngine.