First Activerecord model missing attributes/methods

Hello,

When you say that the first model in the collection does not have the model attributes/methods, is it because you get a NoMethodError exception when you attempt to invoke one of them?

It is normal for a model object not to have the attribute methods (e.g. when dumping the output of object.methods) until you attempt to actually call them. When you attempt to call one of the missing methods in question, ActiveRecord's method_missing handler is triggered and, provided that the method name matches the name of one of the columns defined in the database, the method will be created dynamically and no exception will be risen. If that does not happen it is either because the object is of the wrong class (does not match the model you are expecting to be operating on), or because a plugin or gem is interfering by misbehaving in the method_missing handling chain.

Can you dump into the logs (logger.info or logger.info, depending on your log level) what the attribute-less object instance's self.class.name equal to in? Can you also perform an audit of the gems (and corresponding versions) installed in production vs. locally?

Cheers, V.

@Luke, bad data in the DB should not and will not affect individual object attribute accessor methods. These are welded to the class, and affect models in an all-or-nothing way.

vladr 2009-02-26 07:45:54

Good point. I thought perhaps the attributes were returning nil, but if they're simply not there...That's a different story.

Luke Francl 2009-02-26 18:40:38

@Luke, actually I take that back for Rails 2.2... looking at the 2.2 source code it appears it actually checks against not the columns, but the columns that were actually find'ed (pardon my french) from the db.

vladr 2009-02-27 00:34:38

True, but if the columns are in the result set for one row they would be in the result set for all the rows, wouldn't they? I think you are still correct.

Luke Francl 2009-02-27 00:48:34

We don't know how (form what sources) Kevin is building his @records; I'm not too sure if the "first record is different" is still a problem, we'll see

vladr 2009-02-27 02:44:15

Okay, that makes sense that the first record does not yet have the methods/attributes until it is called. I'm using a aggregating class that has a collection of activerecord models and calling a method and summing up the results. See below in next comment

Kevin Colyar 2009-02-26 17:56:17

Kevin Colyar 2009-02-26 17:58:12

sanity check: can you stick in there a logger call to validate the type of record and whether the record actually has the relevant column?

vladr 2009-02-26 20:10:22

@records.inject(0) {|sum, record| logger.info("#{record.class}: #{record.columns.join(',')}"); sum + (eval("record.#{method.to_s}") || 0) }

vladr 2009-02-26 20:13:48

I couldn't do that for the record itself but I could for the class: MyClass.column_names and it has all the columns I need.I am running ruby 1.8.5 on my debian production server. It's just strange that it's just two attributes it's puking on.

Kevin Colyar 2009-02-26 21:43:23

I did make it so i'm doing a send(method) instead of eval-ing and now I'm getting a ActiveRecord::MissingAttributeError.

Kevin Colyar 2009-02-26 22:09:09

@Kevin, you must really make sure that all your items in @records are of the same class. Also, are they per-chance polymorphic or not (do you have subclasses for the type that @records members should be? is there a class_name column in there?)

vladr 2009-02-26 22:15:05

can you add the modified logger code and share the result? logger.info("#{record.class}: #{record.class.columns.join(',')}"); sum + ...

vladr 2009-02-26 22:15:46

Class: MonthlyConnectedLoadRevenue Columns: id,report_date,new_residential_quantity,...Class: MonthlyConnectedLoadRevenue Columns: (same as above)Class: MonthlyConnectedLoadRevenue Columns: (same as above)Class: MonthlyConnectedLoadRevenue Columns: (same as above)...

Kevin Colyar 2009-02-26 22:39:49

Nope, no polymophic classes here. Would there be some reason those attributes wouldn't be selected in a find?

Kevin Colyar 2009-02-26 22:40:59

..and I assume that the problematic attributes *are* listed in the output above (id,report_date,new_residential_quantity,...) Even if the attributes were not selected, the accessors should exist because they are based on <model>.class.columns (IIRC ActiveRecord's source code)

vladr 2009-02-27 00:18:42

BTW, looking at the Rails code now to see under which conditions, exactly, is the exception risen - what Rails version do you use? 2.2? 2.1.x?

vladr 2009-02-27 00:22:09

OK, in Rails 2.2 it *will* actually raise the exception if an attribute is not selected in a find, as it uses a model's @attributes (not model.class's @columns) to check whether a missing accessor is kosher or not. Can you see the generated SQL queries and see if the missing attributes are SELECTed?

vladr 2009-02-27 00:28:14

Also, what are the names of the mysteriously missing attribute names? Just curious... And I don't suppose you use the :select option in your relationship definition and/or find statement used to populate @records?

vladr 2009-02-27 00:29:49

BTW, instead of __send__'ing, you can just do "sum + (record.read_attribute(method) || 0)" -- this won't crash, but you still have a functional issue if data is not retrieved from the DB

vladr 2009-02-27 00:33:27

Using rails 2.1.0. I'm not using :select, just a find(:all, :conditions => [some conditions]). Offending columns are conversion_wall_heater_quantity and new_residential_electric_heat_revenue.

Kevin Colyar 2009-02-27 16:52:27

Okay, I've figured out my problem. The attribute names on the records are being truncated to 30 characters, yet when I call ClassName.column_names I get the full attribute names back. I'm thinking it's a odbc problem on the production server.

Kevin Colyar 2009-02-27 17:49:25

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First Activerecord model missing attributes/methods

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