infi.clickhouse_orm/docs/querysets.md

Querysets

A queryset is an object that represents a database query using a specific Model. It is lazy, meaning that it does not hit the database until you iterate over its matching rows (model instances). To create a base queryset for a model class, use:

qs = Person.objects_in(database)

This queryset matches all Person instances in the database. You can get these instances using iteration:

for person in qs:
    print person.first_name, person.last_name

Filtering

The filter and exclude methods are used for filtering the matching instances. Calling these methods returns a new queryset instance, with the added conditions. For example:

>>> qs = Person.objects_in(database)
>>> qs = qs.filter(first_name__startswith='V').exclude(birthday__lt='2000-01-01')
>>> qs.conditions_as_sql()
u"first_name LIKE 'V%' AND NOT (birthday < '2000-01-01')"

It is possible to specify several fields to filter or exclude by:

>>> qs = Person.objects_in(database).filter(last_name='Smith', height__gt=1.75)
>>> qs.conditions_as_sql()
u"last_name = 'Smith' AND height > 1.75"

There are different operators that can be used, by passing <fieldname>__<operator>=<value> (two underscores separate the field name from the operator). In case no operator is given, eq is used by default. Below are all the supported operators.

Operator	Equivalent SQL	Comments
eq	field = value
ne	field != value
gt	field > value
gte	field >= value
lt	field < value
lte	field <= value
in	field IN (values)	See below
not_in	field NOT IN (values)	See below
contains	field LIKE '%value%'	For string fields only
startswith	field LIKE 'value%'	For string fields only
endswith	field LIKE '%value'	For string fields only
icontains	lowerUTF8(field) LIKE lowerUTF8('%value%')	For string fields only
istartswith	lowerUTF8(field) LIKE lowerUTF8('value%')	For string fields only
iendswith	lowerUTF8(field) LIKE lowerUTF8('%value')	For string fields only
iexact	lowerUTF8(field) = lowerUTF8(value)	For string fields only

Using the in Operator

The in and not_in operators expect one of three types of values:

• A list or tuple of simple values
• A string, which is used verbatim as the contents of the parentheses
• Another queryset (subquery)

For example if we want to select only people with Irish last names:

# A list of simple values
qs = Person.objects_in(database).filter(last_name__in=["Murphy", "O'Sullivan"])

# A string
subquery = "SELECT name from $db.irishlastname"
qs = Person.objects_in(database).filter(last_name__in=subquery)

# A queryset
subquery = IrishLastName.objects_in(database).only("name")
qs = Person.objects_in(database).filter(last_name__in=subquery)

Counting and Checking Existence

Use the count method to get the number of matches:

Person.objects_in(database).count()

To check if there are any matches at all, you can use any of the following equivalent options:

if qs.count(): ...
if bool(qs): ...
if qs: ...

Ordering

The sorting order of the results can be controlled using the order_by method:

qs = Person.objects_in(database).order_by('last_name', 'first_name')

The default order is ascending. To use descending order, add a minus sign before the field name:

qs = Person.objects_in(database).order_by('-height')

If you do not use order_by, the rows are returned in arbitrary order.

Omitting Fields

When some of the model fields aren't needed, it is more efficient to omit them from the query. This is especially true when there are large fields that may slow the query down. Use the only method to specify which fields to retrieve:

qs = Person.objects_in(database).only('first_name', 'birthday')

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