as_sql ( compiler, connection, function = "CONCAT_WS", template = " %(function)s ('', %(expressions)s )", ** extra_context ) def as_mysql ( self, compiler, connection, ** extra_context ): return super (). The as_vendor() methods should use the function, template,Īrg_joiner, and any other **extra_context parameters toĬustomize the SQL as needed. (sql, params), where sql is the SQL string, and params is Generates the SQL fragment for the database function. as_sql( compiler, connection, function = None, template = None, arg_joiner = None, ** extra_context) ¶ If this attribute is set and the function is called with aĭifferent number of expressions, TypeError will be raised. arity ¶Ī class attribute that denotes the number of arguments the functionĪccepts. arg_joiner ¶Ī class attribute that denotes the character used to join the list ofĮxpressions together. Interpolation with the query parameters in the database cursor. Template attribute because the string is interpolated twice: onceĭuring the template interpolation in as_sql() and once in the SQL Literal % character in the query, quadruple it ( %%%%) in the If you’re constructing SQL like strftime('%W', 'date') and need a template ¶Ī class attribute, as a format string, that describes the SQL that is Specifically, the function will be interpolated as the function The Func API is as follows: class Func( * expressions, ** extra) ¶ function ¶Ī class attribute describing the function that will be generated. See Database Functions for a list of built-in database functions. need_chairs = GreaterThan ( F ( "num_employees" ), F ( "num_chairs" )). filter ( GreaterThan ( F ( "num_employees" ), F ( "num_chairs" ))) # or annotations. ) # Lookup expressions can also be used directly in filters > Company. filter ( company = OuterRef ( "pk" ), salary_gt = 10 )). > from django.db.models import Exists > Company. order_by ( "name_length" ) # Boolean expression can be used directly in filters. > from django.db.models import CharField > from django.db.models.functions import Length > CharField. desc ()) # or using the double underscore lookup syntax. annotate ( num_offerings = Count ( F ( "products" ) + F ( "services" ))) # Expressions can also be used in order_by(), either directly > Company. annotate ( num_products = Count ( F ( "products" ))) # Aggregates can contain complex computations also > Company. annotate ( num_products = Count ( "products" )) > Company. ticker 'GOOG' # Annotate models with an aggregated value. create ( name = "Google", ticker = Upper ( Value ( "goog" ))) # Be sure to refresh it if you need to access the field. chairs_needed 70 # Create a new company using expressions. annotate ( chairs_needed = F ( "num_employees" ) - F ( "num_chairs" )). filter ( num_employees_gt = F ( "num_chairs" )). filter ( num_employees_gt = F ( "num_chairs" ) + F ( "num_chairs" )) # How many chairs are needed for each company to seat all employees? > company = (. filter ( num_employees_gt = F ( "num_chairs" ) * 2 ) > Company. filter ( num_employees_gt = F ( "num_chairs" )) # Find companies that have at least twice as many employees # as chairs. from django.db.models import Count, F, Value > from django.db.models.functions import Length, Upper > from django.db.models.lookups import GreaterThan # Find companies that have more employees than chairs.
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