Get a distinct value from Django QuerySet using MySQL

Question

Does anyone know how to get a distinct value in Django QuerySet? I'm using MySQL db and I couldn't find a solution yet.

The table is:

         ID     WORK_YMD    LINE_NM  MODEL_CODE    MAG_NO             PRODC_MAGT_NO 
        118002  20191015    PBA-21F BN94-14806W A656MAF00001    BR10BN9414806WA656MAE4035
        118003  20191015    PBA-21F BN94-14806W A656MAF00001    BR10BN9414806WA656MAE4027
        118004  20191015    PBA-21F BN94-14806W A656MAF00001    BR10BN9414806WA656MAE4039
        118005  20191015    PBA-21F BN94-14806W A656MAF00001    BR10BN9414806WA656MAE4037
        118006  20191015    PBA-21F BN94-14806W A656MAF00001    BR10BN9414806WA656MAE4038

I want to get the model_code considering a Filter mag_no = "My Variable" Ex:A656MAF00001

I tried something like this, but didn't work.

Magazine.objects.filter(mag_no='A656MAF00001').get('model_code').distinct().order_by()

The error is:

"Too many values to unpack"

you have several PRODC_MAGT_NO for each A656MAF00001 MAG_NO so the distinct clause return all the rows with different value .. are you sure you are looking for distinct and not for min or max PRODC_MAGT_NO related to MAG_NO — ScaisEdge
– ScaisEdge, Commented Oct 16, 2019 at 12:58
Try Magazine.objects.filter(mag_no='A656MAF00001').order_by('model_code).distinct('model_code') — Landcross
– Landcross, Commented Oct 16, 2019 at 13:02
Tks Lancross, but I got the follow error: DISTINCT ON fields is not supported by database backend — HudsonBarroso
– HudsonBarroso, Commented Oct 16, 2019 at 13:09
Hello scaisEdge, my simple aplication is to the user pass the mag_no and django gives model_code, after that a I gonna include other values to save in another table, it's just to validate — HudsonBarroso
– HudsonBarroso, Commented Oct 16, 2019 at 13:13

Nalin Dobhal · Accepted Answer · 2019-10-16 14:27:27Z

2

try:

Magazine.objects.filter(mag_no='A656MAF00001').values('model_code').distinct().order_by('-id')

You can't give arguments to distinct unless you are using Postgres.

From the docs:

On PostgreSQL only, you can pass positional arguments (*fields) in order to specify the names of fields to which the DISTINCT should apply.

Django docs distinct

edit: based on the comment to get the last row.

Magazine.objects.filter(mag_no='A656MAF00001').values('model_code').distinct().last().get('model_code')

edited Oct 16, 2019 at 14:27

answered Oct 16, 2019 at 13:06

Nalin Dobhal

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3 Comments

HudsonBarroso Over a year ago

Really thanks, this definetelly works. But gave a list, possible to get only the last value? I Tried Magazine.objects.filter(mag_no='A656MAF00001').values('model_code').distinct().order_by('-id').last() , but I have {'model_code': 'BN94-14806W'}, how to get only BN94-14806W

HudsonBarroso Over a year ago

Exactly that, Thanks a lot!

Nalin Dobhal Over a year ago

Glad it helped! Please, consider accepting my answer.

Mohammad Abouchama · Accepted Answer · 2019-10-16 14:09:37Z

0

As an improvement on Nalin Dobhal's answer, and in response to your comment to his/her answer, do this:

Magazine.objects.filter(mag_no='A656MAF00001').values('model_code').distinct().order_by('-id').last().get('model_code')

This is because, after invoking last(), you are left with a python dict, and to get a dict's value, you need to use the get('key_name') function. As pointed out here:https://realpython.com/python-dicts/#dgetltkeygt-ltdefaultgt

answered Oct 16, 2019 at 14:09

Mohammad Abouchama

1316 bronze badges

1 Comment

HudsonBarroso Over a year ago

Thank you Mr. Abouchama, now I got 100% that I want.

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