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django note

admin 11月 12, 2020 0

escape, unescape html entities

HTML Escape

try:
    from html import escape  # python 3.x
except ImportError:
    from cgi import escape  # python 2.x

print(escape("<"))

HTML Unescape

try:
    from html import unescape  # python 3.4+
except ImportError:
    try:
        from html.parser import HTMLParser  # python 3.x (<3.4)
    except ImportError:
        from HTMLParser import HTMLParser  # python 2.x
    unescape = HTMLParser().unescape

print(unescape("&gt;"))

log all sql queries

LOGGING = {
    'version': 1,
    'filters': {
        'require_debug_true': {
            '()': 'django.utils.log.RequireDebugTrue',
        }
    },
    'handlers': {
        'console': {
            'level': 'DEBUG',
            'filters': ['require_debug_true'],
            'class': 'logging.StreamHandler',
        }
    },
    'loggers': {
        'django.db.backends': {
            'level': 'DEBUG',
            'handlers': ['console'],
        }
    }
}

log all sql queries

Your understanding is mostly correct. You use select_related when the object that you’re going to be selecting is a single object, so OneToOneField or a ForeignKey.

You use prefetch_related when you’re going to get a “set” of things, so ManyToManyFields as you stated or reverse ForeignKeys. Just to clarify what I mean by “reverse ForeignKeys” here’s an example:

class ModelA(models.Model):
    pass

class ModelB(models.Model):
    a = ForeignKey(ModelA)

ModelB.objects.select_related('a').all() # Forward ForeignKey relationship
ModelA.objects.prefetch_related('modelb_set').all() # Reverse ForeignKey relationship

What’s the difference between select_related and prefetch_related in Django ORM?

How can I see the raw SQL queries Django is running?

Make sure your Django DEBUG setting is set to True. Then, just do this:

>>> from django.db import connection
>>> connection.queries
[{'sql': 'SELECT polls_polls.id, polls_polls.question, polls_polls.pub_date FROM polls_polls',
'time': '0.002'}]

connection.queries includes all SQL statements – INSERTs, UPDATES, SELECTs, etc. Each time your app hits the database, the query will be recorded.

If you are using multiple databases, you can use the same interface on each member of the connections dictionary:

>>> from django.db import connections
>>> connections['my_db_alias'].queries

If you need to clear the query list manually at any point in your functions, just call reset_queries(), like this:

from django.db import reset_queries
reset_queries()

how to modify OneToOneField as inline for admin console?

class NotifyPolicyInlines(admin.StackedInline):
    model = NotifyPolicy

class ServiceAdmin(ModelAdmin):
    filter_horizontal = ('contacts', )
    inlines = [NotifyPolicyInlines, ]

values/values_list 查询结果只返回特定字段

Returns a QuerySet that returns dictionaries, rather than model instances, when used as an iterable.

# This list contains a Blog object.
>>> Blog.objects.filter(name__startswith='Beatles')
<QuerySet [<Blog: Beatles Blog>]>

# This list contains a dictionary.
>>> Blog.objects.filter(name__startswith='Beatles').values()
<QuerySet [{'id': 1, 'name': 'Beatles Blog', 'tagline': 'All the latest Beatles news.'}]>

>>> Entry.objects.values_list('id').order_by('id')
[(1,), (2,), (3,), ...]

>>> Entry.objects.values_list('id', flat=True).order_by('id')
[1, 2, 3, ...]