How do I translate the following to a Django database search?
SELECT column1 FROM TABLE 'my_table' WHERE column2 = 'some text'
So far I've tried this, which is the wrong syntax:
my_table.objects.get(column1,column2 = 'some text')
Get the model instance by column2 using get() and retrieve the value of column1 field:
my_table.objects.get(column2='some text').column1
Note that if the object would not be found, get() throws DoesNotExist exception which you probably want to handle separately. Also, if there would be more than one object found, it would throw MultipleObjectsReturned exception, which is also something you need to think about beforehand.
Alternatively, you can use filter() with values():
my_table.objects.filter(column2='some text').values('column1')
This would return a ValuesQuerySet (think about it as a list of dictionaries).
There are a couple of ways out , here is one :
obj = my_table.objects.get(column2="any_item").column1
Related
I intend to use func function to update a specific JSON field in Sqlalchemy, but I get some problem, here is my code to update field:
self.db.query(TestModel).filter(TestModel.test_id == self._test_id).update(
{field_name: func.json_set(
field_name,
"$." + key,
formatted_val)}
, synchronize_session='fetch'
)
self.db.commit()
I ran the code above and got the error:
sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) malformed JSON
So, I go to check the log, found Sqlalchemy form an SQL clause like that:
UPDATE test_model SET field_name=json_set('field_name', '$.keyname', 'value') WHERE test_model.test_id = 1;
the problem is Sqlalchemy should not use 'field_name' to specific the field it should use field_name to specific the field, and I try to run corrected sql clause below in sql client:
UPDATE test_model SET field_name=json_set(field_name, '$.keyname', 'value') WHERE test_model.test_id = 1;
and it work find
I just want to know how to make the Sqlalchemy form the correct field from 'field_name' to field_name?
You should pass first parameter with a name of model to function func.json_set:
self.db.query(TestModel).filter(TestModel.test_id == self._test_id).update(
{field_name: func.json_set(
TestModel.field_name,
"$." + key,
formatted_val)},
synchronize_session='fetch'
)
self.db.commit()
I want to retrieve all rows matched on multiple partial prase against with a column. My situation can be explained as following raw sql:
SELECT *
FROM TABLENAME
WHERE COLUMN1 LIKE %abc%
OR COLUMN1 LIKE %bcd%
OR COLUMN1 LIKE %def%;
Here, abc, bcd, def are array elements. i.e: array('abc','bcd','def'). Is there any way to write code passing this array to form the above raw sql using cakephp 3?
N.B: I am using mysql as DBMS.
probably you can use Collection to create a proper array, but I think a foreach loop will do the job in the same amount of code. So here is my solution supposing $query stores your Query object
$a = ['abc','bcd','def'];
foreach($a as $value)
{
$or[] = function ($exp, $q) use ($value) {
return $exp->like('column1', '%'.$value.'%');
};
}
$query->where(['or' => $or]);
you could also use orWhere() but I see it will be deprecated in 3.6
Similarly to this question I would like to perform an SQL "like" operation using my own user defined type called "AccountNumber".
The QueryDSL Entity class the field which defines the column looks like this:
public final SimplePath<com.myorg.types.AccountNumber> accountNumber;
I have tried the following code to achieve a "like" operation in SQL but get an error when the types are compared before the query is run:
final Path path=QBusinessEvent.businessEvent.accountNumber;
final Expression<AccountNumber> constant = Expressions.constant(AccountNumber.valueOfWithWildcard(pRegion.toString()));
final BooleanExpression booleanOperation = Expressions.booleanOperation(Ops.STARTS_WITH, path, constant);
expressionBuilder.and(booleanOperation);
The error is:
org.springframework.dao.InvalidDataAccessApiUsageException: Parameter value [7!%%] did not match expected type [com.myorg.types.AccountNumber (n/a)]
Has anyone ever been able to achieve this using QueryDSL/JPA combination?
Did you try using a String constant instead?
Path<?> path = QBusinessEvent.businessEvent.accountNumber;
Expression<String> constant = Expressions.constant(pRegion.toString());
Predicate predicate = Expressions.predicate(Ops.STARTS_WITH, path, constant);
In the end, I was given a tip by my colleague to do the following:
if (pRegion != null) {
expressionBuilder.and(Expressions.booleanTemplate("{0} like concat({1}, '%')", qBusinessEvent.accountNumber, pRegion));
}
This seems to do the trick!
It seems like there is bug/ambiguity. In my case, I need to search by couple fields with different types (String, Number), e.g. SQL looks like:
SELECT * FROM table AS t WHERE t.name = "%some%" OR t.id = "%some%";
My code looks like:
BooleanBuilder where = _getDefaultPredicateBuilder();
BooleanBuilder whereLike = new BooleanBuilder();
for(String likeField: _likeFields){
whereLike = whereLike.or(_pathBuilder.getString(likeField).contains(likeValue));
}
where.and(whereLike);
If first _likeFields is type of String - request works fine, otherwise it throws Exception.
I have a List(Of Hardware) - the List is called HWModels
Class Hardware has the following Properties:
ModelName
Status
CPUStatus
MemoryStatus
DiskStatus
The List is populated by reading a CSV file, once it's populated, I want to return the distinct records based on the ModelName
I've attempted by doing it as follows:
(From a In HWModels Select a.ModelName).Distinct
But this isn't right because I end up with a list of only the ModelName's and nothing else.
How do I get the Distinct function to return all of the other class members within the list?
LINQ to Objects doesn't provide anything to do "distinct by a projection" neatly. You could group by the name and then take the first element in each group, but that's pretty ugly.
My MoreLINQ provides a DistinctBy method though - in C# you'd use:
var distinct = HWModels.DistinctBy(x => x.ModelName).ToList();
Presumably the VB would be something like
Dim distinct = HWModels.DistinctBy(Function(x) x.ModelName).ToList
Apologies for any syntax errors though :(
This will group your objects by the preferred property and then will select the first of each one, removing duplicates.
Dim newlist = HWModels.GroupBy(Function(x) x.ModelName).Select(Function(x) x.First).ToList
suppose we have a model in django defined as follows:
class Literal:
name = models.CharField(...)
...
Name field is not unique, and thus can have duplicate values. I need to accomplish the following task:
Select all rows from the model that have at least one duplicate value of the name field.
I know how to do it using plain SQL (may be not the best solution):
select * from literal where name IN (
select name from literal group by name having count((name)) > 1
);
So, is it possible to select this using django ORM? Or better SQL solution?
Try:
from django.db.models import Count
Literal.objects.values('name')
.annotate(Count('id'))
.order_by()
.filter(id__count__gt=1)
This is as close as you can get with Django. The problem is that this will return a ValuesQuerySet with only name and count. However, you can then use this to construct a regular QuerySet by feeding it back into another query:
dupes = Literal.objects.values('name')
.annotate(Count('id'))
.order_by()
.filter(id__count__gt=1)
Literal.objects.filter(name__in=[item['name'] for item in dupes])
This was rejected as an edit. So here it is as a better answer
dups = (
Literal.objects.values('name')
.annotate(count=Count('id'))
.values('name')
.order_by()
.filter(count__gt=1)
)
This will return a ValuesQuerySet with all of the duplicate names. However, you can then use this to construct a regular QuerySet by feeding it back into another query. The django ORM is smart enough to combine these into a single query:
Literal.objects.filter(name__in=dups)
The extra call to .values('name') after the annotate call looks a little strange. Without this, the subquery fails. The extra values tricks the ORM into only selecting the name column for the subquery.
try using aggregation
Literal.objects.values('name').annotate(name_count=Count('name')).exclude(name_count=1)
In case you use PostgreSQL, you can do something like this:
from django.contrib.postgres.aggregates import ArrayAgg
from django.db.models import Func, Value
duplicate_ids = (Literal.objects.values('name')
.annotate(ids=ArrayAgg('id'))
.annotate(c=Func('ids', Value(1), function='array_length'))
.filter(c__gt=1)
.annotate(ids=Func('ids', function='unnest'))
.values_list('ids', flat=True))
It results in this rather simple SQL query:
SELECT unnest(ARRAY_AGG("app_literal"."id")) AS "ids"
FROM "app_literal"
GROUP BY "app_literal"."name"
HAVING array_length(ARRAY_AGG("app_literal"."id"), 1) > 1
Ok, so for some reason none of the above worked for, it always returned <MultilingualQuerySet []>. I use the following, much easier to understand but not so elegant solution:
dupes = []
uniques = []
dupes_query = MyModel.objects.values_list('field', flat=True)
for dupe in set(dupes_query):
if not dupe in uniques:
uniques.append(dupe)
else:
dupes.append(dupe)
print(set(dupes))
If you want to result only names list but not objects, you can use the following query
repeated_names = Literal.objects.values('name').annotate(Count('id')).order_by().filter(id__count__gt=1).values_list('name', flat='true')