Django-Queryset

Django-Queryset

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  QuerySets Presenter: Ashok KumarSamantray, Mindfire Solutions Date: 26/02/2015
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  Presenter: Ashok KumarSamantray, Mindfire Solutions About me Connect Me: Facebook: https://www.facebook.com/ashokkumar.samantaray.50 Linkedin: https://www.linkedin.com/in/ashokkumarsamantray Google+: https://plus.google.com/+AshokKumarSamantray117/ Contact Me: Email: ashok.samantray@mindfiresolutions.com, mailashok117@gmail.com Skype: mfsi_ashok Ashok Kumar Samantray Python Developer Skills: Python, Django, Tastypie, MySQL, PostgreSQL, MongoDB, JQuery, JavaScript, AJAX
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  Creating Objects Saving Changesto Objects Retrieving Objects Deleting Objects Complex Lookups with Q Objects Q&A AgendaAgenda Presenter: Ashok Kumar Samantray, Mindfire Solutions
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  Creating ObjectsCreating Objects Instanceof a model class represents a record in DB Instanciate a model class using the keyword argument to create an object. Instanciation generates an INSERT query. Call the save() explicitly to run the query. Insert record using the create(), get_or_create() in single step.
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  Saving Changes toObjectsSaving Changes to Objects To save changes to the record already present in the DB use save() Save() performs the update query behind the scenes Saving a Foreignkey works by assigning the object of the right model instance. Saving a ManyToMany field works a little different – from blog.models import Author – joe = Author.objects.create(name="Joe") – entry.authors.add(joe)
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  Retrieving ObjectsRetrieving Objects Letsstart with a simple select query – all_entries = Entry.objects.all() Add conditions using the filter(**kwargs), exclude(**kwargs) – Entry.objects.filter(pub_date__year=2006) – Entry.objects.exclude(pub_date__year=2006)
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  Retrieving Objects(cont.)Retrieving Objects(cont.) Retrievinga single object with get() – Get() works on unique object – It returns the object directly – Raise MultipleObjectsReturned error if more than one item retrieved – e.g.: one_entry = Entry.objects.get(pk=1)
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  Limit, Offset andOrderingLimit, Offset and Ordering A Queryset is iterable. Queryset can be sliced like all other iterables Limit and Offset by slicing the queryset e.g.:- Entry.objects.all()[5:10] Negative indexing is not supported e.g:- Entry.objects.all()[-1] Use of step parameter is allowed and it evaluates the querysets order_by() is used for order the result e.g:- Entry.objects.order_by('headline')
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  Field LookupsField Lookups Itprovides the conditions for where clause in the query Used in the Queryset methods as keyword arguments filter(), exclude(), get(). How does it look? – field__lookuptype=value – Field name and lookuptype joined with a double underscore e.g.: - Entry.objects.filter(pub_date__lte='2006-01-01') Few lookuptypes are exact, iexact, contains etc.
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  Lookup that spanrelationshipsLookup that span relationships This performs the join operations. Use the field name of related fields across models, separated by double underscores e.g.: - Entry.objects.filter(blog__name='Beatles Blog')
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  Complex lookups withQ objectsComplex lookups with Q objects Keyword arguments used in filter() performs AND operation. Q objects comes to rescue for more complex query with OR statements. ~Q is used to negate(NOT) the query. e.g.: - Poll.objects.get( Q(question__startswith='Who'), Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005,5, 6))
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  Deleting ObjectsDeleting Objects Delete()is used for deleting records from the DB This immediately deletes the object Method has no return value e.g.:- Entry.objects.filter(pub_date__year=2005).delete()
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  Some QuerySet methodsSomeQuerySet methods - values() - values_list() - distinct() - only() - defer()
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  Presenter: Ashok KumarSamantray, Mindfire Solutions Question and Answer
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  References LinkReferences Link https://docs.djangoproject.com/en/1.7/topics/db/models/
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  Presenter: Ashok KumarSamantray, Mindfire Solutions Thank you
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