#29155: Using contains lookup with Substr causes modification of second 
parameter
of Substr
-------------------------------------+-------------------------------------
     Reporter:  norac89              |                    Owner:  nobody
         Type:  Bug                  |                   Status:  new
    Component:  Database layer       |                  Version:  2.0
  (models, ORM)                      |
     Severity:  Normal               |               Resolution:
     Keywords:                       |             Triage Stage:  Accepted
    Has patch:  0                    |      Needs documentation:  0
  Needs tests:  0                    |  Patch needs improvement:  0
Easy pickings:  0                    |                    UI/UX:  0
-------------------------------------+-------------------------------------
Changes (by Tim Graham):

 * stage:  Unreviewed => Accepted


Old description:

> My model:
>

> {{{
> class User(models.Model):
>     field1 = models.Charfield(max_length=120)
>     field2 = models.Charfield(max_length=120)
> }}}
>
> Tried querying the model to get User instances in which field2 start with
> the three first characters of field1.
> Tried the following:
>
> {{{
> User.objects.filter(field2__startswith=Substr(F('field1'), 1, 3))
> }}}
>
> I m getting the following error
>
> {{{
> psycopg2.DataError: invalid input syntax for integer: "1%"
> LINE 1: ...(REPLACE(REPLACE((SUBSTRING("test_user"."field1", '1%',
> 3)),...
> }}}
>
> The second parameter of the substr function seems to be replaced with
> '1%'.

New description:

 My model:


 {{{
 class User(models.Model):
     field1 = models.CharField(max_length=120)
     field2 = models.CharField(max_length=120)
 }}}

 Tried querying the model to get User instances in which field2 start with
 the three first characters of field1.
 Tried the following:

 {{{
 User.objects.filter(field2__startswith=Substr(F('field1'), 1, 3))
 }}}

 I m getting the following error

 {{{
 psycopg2.DataError: invalid input syntax for integer: "1%"
 LINE 1: ...(REPLACE(REPLACE((SUBSTRING("test_user"."field1", '1%', 3)),...
 }}}

 The second parameter of the substr function seems to be replaced with
 '1%'.

--

Comment:

 I'm attaching a test for Django's test suite that fails (on PostgreSQL but
 not SQLite) as of ba37ee9ef882deb8e917f1cae0c586a0a275e731.

-- 
Ticket URL: <https://code.djangoproject.com/ticket/29155#comment:1>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.

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