sql "LIKE" equivalent in django query

Question

What is the equivalent of this SQL statement in django?

SELECT * FROM table_name WHERE string LIKE pattern;

How do I implement this in django? I tried

result = table.objects.filter( pattern in string )

But that did not work. How do i implement this?

Solution 1

Use __contains or __icontains (case-insensitive):

result = table.objects.filter(string__contains='pattern')

The SQL equivalent is

SELECT ... WHERE string LIKE '%pattern%';

@Dmitri's answer below covers patterns like 'pattern%' or '%pattern'

Solution 2

contains and icontains mentioned by falsetru make queries like SELECT ... WHERE headline LIKE '%pattern%

Along with them, you might need these ones with similar behavior: startswith, istartswith, endswith, iendswith

making

SELECT ... WHERE headline LIKE 'pattern%

or

SELECT ... WHERE headline LIKE '%pattern

Solution 3

This can be done with Django's custom lookups. I have made the lookup into a Django-like-lookup application. After installing it the __like lookup with the % and _ wildcards will be enabled.

All the necessary code in the application is:

from django.db.models import Lookup
from django.db.models.fields import Field


@Field.register_lookup
class Like(Lookup):
    lookup_name = 'like'

    def as_sql(self, compiler, connection):
        lhs, lhs_params = self.process_lhs(compiler, connection)
        rhs, rhs_params = self.process_rhs(compiler, connection)
        params = lhs_params + rhs_params
        return '%s LIKE %s' % (lhs, rhs), params

Solution 4

result = table.objects.filter(string__icontains='pattern')

Case insensitive search for string in a field.

Solution 5

In order to preserve the order of the words as in the sql LIKE '%pattern%' statement I use iregex, for example:

qs = table.objects.filter(string__iregex=pattern.replace(' ', '.*'))

string methods are immutable so your pattern variable will not change and with .* you'll be looking for 0 or more occurrences of any character but break lines.

By using the following to iterate over the pattern words:

qs = table.objects
for word in pattern.split(' '):
    qs = qs.filter(string__icontains=word)

the order of the words in your pattern will not be preserved, for some people that could work but in the case of trying to mimic the sql like statement I'll use the first option.

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Comments

[Hitesh Garg]

And for case insensitive search use __icontains -> result = table.objects.filter(string__icontains='pattern')

[kasperd]

This answer only covers a subset of the possible patterns. It wouldn't handle a pattern like %a%b%.

[Mr. Lance E Sloan]

Nice, but the same answer had already been given almost three years earlier.

[Mr. Lance E Sloan]

@kasperd, try: result = table.objects.filter(string__contains='a').filter(string__co‌​ntains='b')

[kasperd]

@LS That would match ba which LIKE %a%b% would not.

[Underoos]

@falsetru What about cases like these? - stackoverflow.com/questions/57004942/…

[medley56]

This answer is incomplete for the reasons stated above. It should also include the information in @Dmitry's answer.

[falsetru]

@medley56, OP mentioned pattern in string which correspond to __contains. And I thought people will follow the link in the answer, they can find another field lookup options. As Dmitriy already answered, I'll leave my answer as is. Thank you for your feedback.

[Lutz Prechelt]

This is the proper answer to the question, unlike the accepted answer.

[Lutz Prechelt]

See the answer by Petr Dlouhý below for a proper answer that handles all SQL LIKE patterns.

[wihlke]

This is pretty cool, but is there any risk of user being able to pass dirty data into the query?

[wihlke]

You might want to make the replacement .*? to have lazy matching and not consume the whole string.

[msanjay]

@falsetru The OP's question is where string like pattern, and the pattern can be anything. So I spent quite a bit of time putting in a % in the pattern and wondering why it didn't work till I read Dmitri's answer. So I suggest its worth mentioning the point here. Thanks