The following is to get 1 record out of database by matching enum type.
TYPES = (
('ABC_ABC', 'abc abc'),
('XYZ_XYZ', 'xyz xyz'),
)
class Hello(models.Model):
type = models.CharField(max_length=8, choices=TYPES, blank=True)
database:
'1', 'ABC_ABC', 'other data'
Queryset:
qset = Q(type__in=('ABC_ABC'))
hello = models.Hello.objects.filter(qset)
Output:
print('count: {}'.format(hello.count()))
Result is 0. It should be 1. What's wrong?
Try changing your Q filter as follow:
qset = Q(type='ABC_ABC')
Explanations:
When using in lookup, django expects an iterable. As you provided only one value, I suspect, it tried to iterate over the string 'ABC_ABC' which is why you didn't get any hit.
If you really want to use the in lookup, which is useless in this case, you should add a comma in to force creating a 1-tuple.
qset = Q(type__in=('ABC_ABC',))
Further thoughts
As this query is quite basic, using a Q object is superfluous. You can simply call
.filter(type='ABC_ABC')
Related
I’m a beginner in Laravel but have a problem at first. I wrote this query and I’m waiting for Sonya Bins as result but unexpectedly I see ["Sonya Bins"]. what’s the problem?
Route::get('products', function () {
$articles=DB::table('users')->where('id','2')->get()->pluck('name');
return view('products',compact('articles'));
});
pluck will return array if you want to get only single value then use value
// will return array
$articles=DB::table('users')->where('id','2')->get()->pluck('name');
//will return string
$articles=DB::table('users')->where('id','2')->value('name');
// output Sonya Bins
here is an example from the documentation:
if you don't even need an entire row, you may extract a single value from a record using the value method. This method will return the value of the column directly:
$email = DB::table('users')->where('name', 'John')->value('email');
Read more about it here
Hope it helps.
Thanks
pluck() used to return a String before Laravel 5.1, but now it returns an array.
The alternative for that behavior now is value()
Try this:
Route::get('products', function () {
$articles=DB::table('users')->where('id','2')->get()->value('name');
return view('products',compact('articles'));
});
I think it's easier to use the Model + find function + value function.
Route::get('products', function () {
$articles = User::find(2)->value('name');
return view('products',compact('articles'));
});
pluck will return the collection.
I think id is your primary key.
You can just get the first record, and call its attribute's name:
DB::table('users')->where('id','2')->first()->name;
or
DB::table('users')->find(2)->name;
First thing is that you used invalid name for what you pass to view - you don't pass articles but user name.
Second thing is that you use get method to get results instead of first (or find) - you probably expect there is only single user with id = 2.
So to sum up you should use:
$userName = DB::table('users')->find(2)->name;
return view('products',compact('userName'));
Of course above code is for case when you are 100% sure there is user with id = 2 in database. If it might happen there won't be such user, you should use construction like this:
$userName = optional(DB::table('users')->find(2))->name;
($userName will be null if there is no such record)
or
$userName = optional(DB::table('users')->find(2))->name ?? 'No user';
in case you want to use custom string.
I have an Array of [Long, Q] and would like to make a binary search on it. I tried below :
import scala.collection.Searching._
class Q (val b:Double, val a:Double)
val myArray = Array(5L -> new Q(1,2), 6L-> new Q(6,9), 7L-> new Q(7,6))
val i = myArray.search(6L).insertionPoint
but had this error
No implicit Ordering defined for Any
Unspecified value parameter ord.
I understand that I need to specify an odering rule for this collection Array[(Long,Q)] but can't figure this out myself.
Please help
Signature of search is search[B >: A](elem: B)(implicit ord: Ordering[B]). You've got an array of type [Long, Q]. So in order for the compiler to infer Ordering correctly, you'd have to invoke search like that:
myArray.search(6L-> q/*Q(6,9)*/)(Ordering.by(_._1)) //ordering by the first value in a tuple.
and what you're doing is: myArray.search(6L). If I understand correctly what you're trying to do, it's probably to find both value and position in the array.
You could solve it by using two separate data structures:
keys could be stored in the array, like this:
val myArray = Array(5L, 6L, 7L).toList
myArray.search(6L).insertionPoint
and if you'd need values, you could use map which would work as a dictionary:
val dictionary = Map(
5L -> new Q(1,2),
6L-> new Q(6,9),
7L-> new Q(7,6)
)
EDIT:
Actually, I noticed something like that would work:
val dummy = new Q(0,0) //any instance of Q
myArray.search(6L-> dummy)(Ordering.by(_._1)).insertionPoint //1
It works since for lookup of the insertion point Ordering is used and no equality test is performed.
Executing below code returns the result that contains the element of type hashmap instead of type T (the basicDBList coming from mongoDB does not have "_class" attribute:
com.mongodb.BasicDBList basicDBList = // output of mongoDB query;
List<T> result = mongoOperations.getConverter().read(List.class, basicDbList);
Is there any way to provide type information of List to the read method ?
Not exactly clear what you're trying to achieve, but if you acquired your BasicDBList by calling the getRawResults().get("result") of an AggregationResults instance, you can instead call getMappedResults:
Aggregation aggregation = Aggregation.newAggregation(...);
AggregationResults<Foo> r = mongoTemplate.aggregate(aggregation, "foos", Foo.class);
List<Foo> foos = r.getMappedResults();
According to the Dapper documentation, you can get a dynamic list back from dapper using below code :
var rows = connection.Query("select 1 A, 2 B union all select 3, 4");
((int)rows[0].A)
.IsEqualTo(1);
((int)rows[0].B)
.IsEqualTo(2);
((int)rows[1].A)
.IsEqualTo(3);
((int)rows[1].B)
.IsEqualTo(4);
What is however the use of dynamic if you have to know the field names and datatypes of the fields.
If I have :
var result = Db.Query("Select * from Data.Tables");
I want to be able to do the following :
Get a list of the field names and data types returned.
Iterate over it using the field names and get back data in the following ways :
result.Fields
["Id", "Description"]
result[0].values
[1, "This is the description"]
This would allow me to get
result[0].["Id"].Value
which will give results 1 and be of type e.g. Int 32
result[0].["Id"].Type --- what datattype is the value returned
result[0].["Description"]
which will give results "This is the description" and will be of type string.
I see there is a results[0].table which has a dapperrow object with an array of the fieldnames and there is also a result.values which is an object[2] with the values in it, but it can not be accessed. If I add a watch to the drilled down column name, I can get the id. The automatically created watch is :
(new System.Collections.Generic.Mscorlib_CollectionDebugView<Dapper.SqlMapper.DapperRow>(result as System.Collections.Generic.List<Dapper.SqlMapper.DapperRow>)).Items[0].table.FieldNames[0] "Id" string
So I should be able to get result[0].Items[0].table.FieldNames[0] and get "Id" back.
You can cast each row to an IDictionary<string, object>, which should provide access to the names and the values. We don't explicitly track the types currently - we simply don't have a need to. If that isn't enough, consider using the dapper method that returns an IDataReader - this will provide access to the raw data, while still allowing convenient call / parameterization syntax.
For example:
var rows = ...
foreach(IDictionary<string, object> row in rows) {
Console.WriteLine("row:");
foreach(var pair in row) {
Console.WriteLine(" {0} = {1}", pair.Key, pair.Value);
}
}
I'm trying to figure out how to execute a custom query with Castle ActiveRecord.
I was able to run simple query that returns my entity, but what I really need is the query like that below (with custom field set):
select count(1) as cnt, data from workstationevent where serverdatetime >= :minDate and serverdatetime < :maxDate and userId = 1 group by data having count(1) > :threshold
Thanks!
In this case what you want is HqlBasedQuery. Your query will be a projection, so what you'll get back will be an ArrayList of tuples containing the results (the content of each element of the ArrayList will depend on the query, but for more than one value will be object[]).
HqlBasedQuery query = new HqlBasedQuery(typeof(WorkStationEvent),
"select count(1) as cnt, data from workstationevent where
serverdatetime >= :minDate and serverdatetime < :maxDate
and userId = 1 group by data having count(1) > :threshold");
var results =
(ArrayList)ActiveRecordMediator.ExecuteQuery(query);
foreach(object[] tuple in results)
{
int count = (int)tuple[0]; // = cnt
string data = (string)tuple[1]; // = data (assuming this is a string)
// do something here with these results
}
You can create an anonymous type to hold the results in a more meaningful fashion. For example:
var results = from summary in
(ArrayList)ActiveRecordMediator.ExecuteQuery(query)
select new {
Count = (int)summary[0], Data = (string)summary[1]
};
Now results will contain a collection of anonymous types with properties Count and Data. Or indeed you could create your own summary type and populate it out this way too.
ActiveRecord also has the ProjectionQuery which does much the same thing but can only return actual mapped properties rather than aggregates or functions as you can with HQL.
Be aware though, if you're using ActiveRecord 1.0.3 (RC3) as I was, this will result in a runtime InvalidCastException. ActiveRecordMediator.ExecuteQuery returns an ArrayList and not a generic ICollection. So in order to make it work, just change this line:
var results = (ICollection<object[]>) ActiveRecordMediator.ExecuteQuery(query);
to
var results = (ArrayList) ActiveRecordMediator.ExecuteQuery(query);
and it should work.
Also note that using count(1) in your hql statement will make the query return an ArrayList of String instead of an ArrayList of object[] (which is what you get when using count(*).)
Just thought I'd point this out for the sake of having it all documented in one place.