Getting error - Cannot add or update a child row: a foreign key constraint fails for a legacy database in django

Question

I recently ported from raw php to django and had to incorporate my legacy database into it. I used the inspectdb command to construct the models out of the database and everything was working fine.

Recently I decided to add the functionality of like and set to favorite. So I added a new table as shown below.

class SongCollection(models.Model):
    song_name = models.TextField()
    song_type = models.CharField(max_length=765)
    likes = models.IntegerField(default=0)

    class Meta:
        db_table = u'songcollection'


class likeSong(models.Model):

    user = models.ForeignKey(User)
    company = models.ForeignKey(SongCollection)

The first one is my original class and the other one is for storing which user has liked which song. I am using the exact structure for like in my other applications completely developed in django and they are working fine. But when I try to add an object to likeSong I get the following error.

Cannot add or update a child row: a foreign key constraint fails

I tried to add this object from MySql command line as well, in order to check if this was a Django error but it failed there also. Can anybody help me in understanding in what actually is wrong here?

score 8 · Accepted Answer · answered Jan 14 '12 at 06:34

I have figured out what the problem is, as I said I had dumped the legacy database into my new django project. The older tables were created using phpMyAdmin and the storage engine type for the table was of MyISAM however the new tables created my django had a storage type of innodb.

As a result there was an incompatibility between the two tables and whenever I added a tuple in the newer table, the foreign key constraint failed as it did not find an equivalent object in the referenced table because the referenced table did not have the same storage engine.

I changed the storage engine of the older table to innodb and now it is working fine. I used this command to change

ALTER TABLE ourquestions ENGINE = innodb

Hope it helps somebody.

score 1 · Answer 2 · answered Jan 10 '12 at 11:22

1

This error happens when you want to delete , update or make changes on a table in your database that has a relation with another table. In this case, you have to make your changes in the main table (Primary) and after that, change your records in the second table.

heck your databse tables and relations.

Please tell me the result

answered Jan 10 '12 at 11:22

Mohammad Saberi

12,864
27
75
127

My `like` logic is like this: When a user clicks on the like button for that song, then an entry is created in the `likeSong` table which has two foreign keys, one to the user and one to song. I am not making any changes in the table referenced by the `foreign-key` and the exact same thing works for me on other models, but fails on this model which is basically a legacy database – Sachin Jan 10 '12 at 11:26

Getting error - Cannot add or update a child row: a foreign key constraint fails for a legacy database in django

2 Answers2