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PODjango model inheritance error with PostgreSQL
 

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  1. PODjango model inheritance error with PostgreSQL
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    <p>I'm switching from a MySQL backend to a PostgreSQL backend and am running into some model inheritance issues. Here is an example of the models:</p> <pre><code>class Parent(models.Model): key = models.Charfield(...) value = models.Charfield(...) content_type = models.ForeignKey(ContentType) object_id = models.CharField(max_length=200) content_object = generic.GenericForeignKey('content_type', 'object_id') class Child1(Parent): pass class Child2(Parent): pass </code></pre> <p>The reason we have two child classes like this is, we're simulating two key/value pairs in another model, and wanted to separated them into two tables for an easier lookup. The Generic FKs were also for attaching this to other models. This inheritance setup works fine in MySQL, but when I switched it to PostgreSQL, I get an error when trying to run our tests (but syncdb works fine). It's as if Django is OK with the relationship but PostgreSQL doesn't like the SQL being generated. When I look at what's being generated from syncdb I see this:</p> <pre><code>CREATE TABLE "myapp_parent" ( "id" serial NOT NULL PRIMARY KEY, "key" varchar(200) NOT NULL, "value" varchar(200) NOT NULL, "content_type_id" integer NOT NULL REFERENCES "django_content_type" ("id") DEFERRABLE INITIALLY DEFERRED, "object_id" varchar(200) NOT NULL); CREATE TABLE "myapp_child1" ( "parent_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "myapp_parent" ("id") DEFERRABLE INITIALLY DEFERRED); CREATE TABLE "myapp_child2" ( "parent_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "myapp_parent" ("id") DEFERRABLE INITIALLY DEFERRED); </code></pre> <p>So everything looks right, then when I run my tests I get this:</p> <pre><code>Error: Database test_myapp couldn't be flushed. Possible reasons: * The database isn't running or isn't configured correctly. * At least one of the expected database tables doesn't exist. * The SQL was invalid. Hint: Look at the output of 'django-admin.py sqlflush'. That's the SQL this command wasn't able to run. The full error: column "id" of relation "myapp_child1" does not exist </code></pre> <p>When I run flush:</p> <pre><code>SELECT setval(pg_get_serial_sequence('"myapp_child1"','id'), 1, false); </code></pre> <p>I've tried manually adding an ID field as the primary key in the child model but Django throws an error saying it conflicts with the Parent's ID field. How do I fix this so PostgreSQL likes it? And thanks in advance. </p>
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    1. COWhen you use MySQL, does Django create a column named "id" in table "myapp_child1"?
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      1. USMike Sherrill 'Cat Recall'
    2. CONo it does not. In both DBs the only column is parent_ptr_id
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    3. COSounds like a Django bug. I looked briefly through their ticketing system, but I didn't see it. Maybe you should report it. (But wait a bit to see if anyone else here on SO might know more than I do.)
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      1. USMike Sherrill 'Cat Recall'
 

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