how can I get say the previous 5 objects before x object when I know x's id?
For example I get the 5 last objects of a model like this
numPosts = Post.objects.filter(topic=topic).count()
pre = numPosts - 5
posts = Post.objects.filter(topic=topic).order_by('date')[pre:numPosts]
Now if I know the id of the post with the oldest date, how can I get the 5 next objects, or less if there are not enough?
http://docs.djangoproject.com/en/dev/topics/db/queries/#limiting-querysets
posts = Post.objects.filter(topic=topic).order_by('date')
x = posts.get(id=id)
next_five = posts.filter(date__lt=x.date)[:5]
should return the next 5 (or less) objects
Related
How can i filter 12 random objects from a model in django .
I tried to do this but It does not work and It just returned me 1 object.
max = product.objects.aggregate(id = Max('id'))
max_p = int(max['id'])
l = []
for s in range(1 , 13):
l.append(random.randint(1 , max_p))
for i in l:
great_proposal = product.objects.filter(id=i)
products = product.objects.all().order_by('-id')[:50]
great_proposal1 = random.sample(list(products) , 12)
Hi . It worked with this code !
Try this:
product.objects.order_by('?')[:12]
The '?' will "sort" randomly and "[:12]" will get only 12 objects.
I'm pretty sure the code is correct, but maybe you did not realize that you're just using great_proposal as variable to save the output, which is not an array, and therefore only returns one output.
Try:
result_array = []
for i in l:
result_array.append(product.objects.filter(index=i))
I have seen similar questions. This one is the most similar that I've found:
Python converting a list into a dict with a value of 1 for each key
The difference is that I need the dict keys to be unique and ordered keyword arguments.
I am trying to feed the list of links I've generated through a scraper into a request command. I understand the request.get() function only takes a URL string or kwarg parameters - hence my need to pair the list of links with keyword arguments that are ordered.
terms = (input(str('type boolean HERE -->')))
zipcity = (input(str('type location HERE -->')))
search = driver.find_element_by_id('keywordsearch')
search.click()
search.send_keys('terms')
location = driver.find_element_by_id('WHERE')
location.click()
location.send_keys('zipcity')
clickSearch = driver.find_element_by_css_selector('#buttonsearch-button')
clickSearch.click()
time.sleep(5)
cv = []
cvDict = {}
bbb = driver.find_elements_by_class_name('user-name')
for plink in bbb:
cv.append(plink.find_element_by_css_selector('a').get_attribute('href'))
cvDict = {x: 1 for x in cv}
print(cvDict)
SOLVED: (for now). Somehow figured it out myself. That literally never happens. Lucky day I guess!
cvDict = {'one': cv[:1],
'tw': cv[:2],
'thr': cv[:3],
'fou': cv[:4],
'fiv': cv[:5],
'six': cv[:6],
'sev': cv[:7],
'eig': cv[:8],
'nin': cv[:9],
'ten': cv[:10],
'ele': cv[:11],
'twe': cv[:12],
'thi': cv[:13],
'fourteen': cv[:14],
'fifteen': cv[:15],
'sixteen': cv[:16],
'seventeen': cv[:17],
'eighteen': cv[:18],
'nineteen': cv[:19],
'twent': cv[:20],
}
I can run a query in two different ways to return a Relation.
When I interrogate the size of the Relation one query gives a Fixnum as expected the other gives a Hash which is a hash of each value in the Relations Group By statement with the number of occurrences of each.
In Rails 3 I assume it always returned a Fixnum as I never had a problem whereeas with Rails 4 it sometimes returns a Hash and a statement like Rel.size.zero? gives the error:
undefined method `zero?' for {}:Hash
Am I best just using the .blank? method to check for zero records to be sure of avoiding unexpected errors?
Here is a snippet of code with looging statements for the two queries and the resulting log
CODE:
assessment_responses1=AssessmentResponse.select("process").where("client_id=? and final = ?",self.id,false).group("process")
logger.info("-----------------------------------------------------------")
logger.info("assessment_responses1.class = #{assessment_responses1.class}")
logger.info("assessment_responses1.size.class = #{assessment_responses1.size.class}")
logger.info("assessment_responses1.size value = #{assessment_responses1.size}")
logger.info("............................................................")
assessment_responses2=AssessmentResponse.select("distinct process").where("client_id=? and final = ?",self.id,false)
logger.info("assessment_responses2.class = #{assessment_responses2.class}")
logger.info("assessment_responses2.size.class = #{assessment_responses2.size.class}")
logger.info("assessment_responses2.size values = #{assessment_responses2.size}")
logger.info("-----------------------------------------------------------")
LOG
-----------------------------------------------------------
assessment_responses1.class = ActiveRecord::Relation::ActiveRecord_Relation_AssessmentResponse
(0.5ms) SELECT COUNT(`assessment_responses`.`process`) AS count_process, process AS process FROM `assessment_responses` WHERE `assessment_responses`.`organisation_id` = 17 AND (client_id=43932 and final = 0) GROUP BY process
assessment_responses1.size.class = Hash
CACHE (0.0ms) SELECT COUNT(`assessment_responses`.`process`) AS count_process, process AS process FROM `assessment_responses` WHERE `assessment_responses`.`organisation_id` = 17 AND (client_id=43932 and final = 0) GROUP BY process
assessment_responses1.size value = {"6 Month Review(1)"=>3, "Assessment(1)"=>28, "Assessment(2)"=>28}
............................................................
assessment_responses2.class = ActiveRecord::Relation::ActiveRecord_Relation_AssessmentResponse
(0.5ms) SELECT COUNT(distinct process) FROM `assessment_responses` WHERE `assessment_responses`.`organisation_id` = 17 AND (client_id=43932 and final = 0)
assessment_responses2.size.class = Fixnum
CACHE (0.0ms) SELECT COUNT(distinct process) FROM `assessment_responses` WHERE `assessment_responses`.`organisation_id` = 17 AND (client_id=43932 and final = 0)
assessment_responses2.size values = 3
-----------------------------------------------------------
size on an ActiveRecord::Relation object translates to count, because the former tries to get the count of the Relation. But when you call count on a grouped Relation object, you receive a hash.
The keys of this hash are the grouped column's values; the values of this hash are the respective counts.
AssessmentResponse.group(:client_id).count # this will return a Hash
AssessmentResponse.group(:client_id).size # this will also return a Hash
This is true for the following methods: count, sum, average, maximum, and minimum.
If you want to check for rows being present or not, simply use exists? i.e. do the following:
AssessmentResponse.group(:client_id).exists?
Instead of this:
AssessmentResponse.group(:client_id).count.zero?
I'm new to OCaml and i'm trying to understand the concept of mutable record field.
I'd like to create an array of records and that record contains a boolean mutable field. So i did something like:
type t = {i: int; mutable b: bool};;
I want to be able to change the value of the 'b' field of the record, so i put it mutable
let m = Array.make 10 ({i = 5; b = false});;
Here i try to set the b field of the record located at the first index of my array :
(Array.get m 0).b <- true;;
The problem is want i do it, it will set 'b' field of all the records of the array, and this is not what i want.
Does the mutable fields of a same record share the same memory emplacement? How can i do to change the value of the 'b' field of a specific record?
As the documentation states, Array.make creates an array whose elements are all physically equal. That's not a problem if these elements are immutable, but as you saw, you have to take that into account if they are mutable.
What you can do is use Array.init, to create a different object for every cell of your array:
let m = Array.init 10 (fun _ -> {i = 5; b = false});;
I am seeing a problem with some Scala 2.7.7 code I'm working on, that should not happen if it the equivalent was written in Java. Loosely, the code goes creates a bunch of card players and assigns them to tables.
class Player(val playerNumber : Int)
class Table (val tableNumber : Int) {
var players : List[Player] = List()
def registerPlayer(player : Player) {
println("Registering player " + player.playerNumber + " on table " + tableNumber)
players = player :: players
}
}
object PlayerRegistrar {
def assignPlayersToTables(playSamplesToExecute : Int, playersPerTable:Int) = {
val numTables = playSamplesToExecute / playersPerTable
val tables = (1 to numTables).map(new Table(_))
assert(tables.size == numTables)
(0 until playSamplesToExecute).foreach {playSample =>
val tableNumber : Int = playSample % numTables
tables(tableNumber).registerPlayer(new Player(playSample))
}
tables
}
}
The PlayerRegistrar assigns a number of players between tables. First, it works out how many tables it will need to break up the players between and creates a List of them.
Then in the second part of the code, it works out which table a player should be assigned to, pulls that table from the list and registers a new player on that table.
The list of players on a table is a var, and is overwritten each time registerPlayer() is called. I have checked that this works correctly through a simple TestNG test:
#Test def testRegisterPlayer_multiplePlayers() {
val table = new Table(1)
(1 to 10).foreach { playerNumber =>
val player = new Player(playerNumber)
table.registerPlayer(player)
assert(table.players.contains(player))
assert(table.players.length == playerNumber)
}
}
I then test the table assignment:
#Test def testAssignPlayerToTables_1table() = {
val tables = PlayerRegistrar.assignPlayersToTables(10, 10)
assertEquals(tables.length, 1)
assertEquals(tables(0).players.length, 10)
}
The test fails with "expected:<10> but was:<0>". I've been scratching my head, but can't work out why registerPlayer() isn't mutating the table in the list. Any help would be appreciated.
The reason is that in the assignPlayersToTables method, you are creating a new Table object. You can confirm this by adding some debugging into the loop:
val tableNumber : Int = playSample % numTables
println(tables(tableNumber))
tables(tableNumber).registerPlayer(new Player(playSample))
Yielding something like:
Main$$anon$1$Table#5c73a7ab
Registering player 0 on table 1
Main$$anon$1$Table#21f8c6df
Registering player 1 on table 1
Main$$anon$1$Table#53c86be5
Registering player 2 on table 1
Note how the memory address of the table is different for each call.
The reason for this behaviour is that a Range is non-strict in Scala (until Scala 2.8, anyway). This means that the call to the range is not evaluated until it's needed. So you think you're getting back a list of Table objects, but actually you're getting back a range which is evaluated (instantiating a new Table object) each time you call it. Again, you can confirm this by adding some debugging:
val tables = (1 to numTables).map(new Table(_))
println(tables)
Which gives you:
RangeM(Main$$anon$1$Table#5492bbba)
To do what you want, add a toList to the end:
val tables = (1 to numTables).map(new Table(_)).toList
val tables = (1 to numTables).map(new Table(_))
This line seems to be causing all the trouble - mapping over 1 to n gives you a RandomAccessSeq.Projection, and to be honest, I don't know how exactly they work, but a bit less clever initialising technique does the job.
var tables: Array[Table] = new Array(numTables)
for (i <- 0 to numTables) tables(i) = new Table(i)
Using the first initialisation method I wasn't able to change the objects (just like you), but using a simple array everything seems to be working.