Improve performance in operation Django ORM

Orm enhance operational performance point of attention

 

Optimization one: try not to check the object, use values ​​is to use values

Direct result of using an object query is 5 sql statement

def youhua(request):
    # 使用对象查
    obj_list = models.Book.objects.all()
    for obj in obj_list:
        print(obj.title,obj.pubs.name)
        
    return render(request,"youhua.html")

Use values ​​query is only executed one sql, will automatically connect table query

def youhua(request):
    # 使用values
    obj_list = models.Book.objects.values('title', 'pubs__name')
    for obj in obj_list:
        print(obj['title'], obj['pubs__name'])

    return render(request,"youhua.html")

Optimization two: select_related ( 'classes')

使用select_related('classes')

Applies to: many-to-one to one query add select_related () method, in brackets is a foreign key field. It will be even table query

def youhua(request):
    # 使用对象查
    obj_list = models.Book.objects.all().select_related('pubs')
    for obj in obj_list:
        print(obj.title, obj.pubs.name)

    return render(request,"youhua.html")

Optimization three: prefetch_related ()

Use prefetch_related (), many to one,

def youhua(request):

    obj_list = models.Book.objects.all().prefetch_related("pubs")
    for obj in obj_list:
        print(obj.title,obj.pubs.name)

    return render(request,"youhua.html")

Use prefetch_related (), many to many,

def youhua(request):

    obj_list = models.Book.objects.all()
    for obj in obj_list:
        print(obj.title,obj.authors.all())

    return render(request,"youhua.html")

def youhua(request):

    obj_list = models.Book.objects.all().prefetch_related("authors")
    for obj in obj_list:
        print(obj.title,obj.authors.all())

    return render(request,"youhua.html")

Optimization of a Four: only () specify the query field

The case of direct queries, will check out all fields

def youhua(request):

    obj_list = models.Book.objects.all()
    for obj in obj_list:
        print(obj.title)

    return render(request,"youhua.html")

Some fields specified query query, use only specified fields will be found that the field we need.

def youhua(request):

    obj_list = models.Book.objects.all().only('title')
    for obj in obj_list:
        print(obj.title)

    return render(request,"youhua.html")

Optimization five: defer () specify the exclusion of certain fields opposite and only query

If the field we need more, no less, can be used to exclude defer

def youhua(request):

    obj_list = models.Book.objects.all().defer('title')
    for obj in obj_list:
        print(obj.pubtime)

    return render(request,"youhua.html")

Note: If you exclude the field, but also check the query will increase the burden, of course, query fields outside the specified field will increase the burden on the query.