After adding a new Core Data model version to my app, I performed a lightweight migration, apparently successfully. The migrated file loaded fine, but upon the first attempt to access an attribute via a particular relationship, the app crashes with an NSRangeException: '*** -[__NSArrayM objectAtIndex:]: index 4294967295 beyond bounds [0 .. 35]'. This relationship worked fine prior to the migration. I know from other posts here that 4294967295 is really -1, but the only thing I can identify with 36 items in my app/data is that there are 36 total entities in the data model (for reference, the relationship that's being fetched has 58 items in its table).
The question:
My question is: based on the error I'm getting and the troubleshooting I've done below, is there a type of schema change that could pass the lightweight migration, but corrupt the data along the way, leading to the noted exception? I'm going to try breaking down the migration into smaller chunks over several versions to either isolate or avoid the issue, but it would be nice to be able to focus on specific schema changes that might be at fault.
The failure:
The failure occurs with the following code in "myobject":
[[self object2] text];
The object2 relationship is to-one, non-optional both ways and neither the forward nor inverse relationship was changed between data models. The text attribute is likely not relevant because when the error occurs, awakeFromFetch is not reached in object2. If I assign [self object2] to a variable prior to the above statement, the assignment is successful and reports data: <fault>.
The database:
Looking at the database in sqlite3, I notice the following:
The index values for the forward and inverse relationships appear to be correct in each table.
The object2 table has two columns for the inverse relationship instead of the one prior to migration (ZMYOBJECT as before and the additional Z2_MYOBJECT, which is empty for all rows). No other relationship were added to explain this column.
In the Z_PRIMARYKEY table, all entries post-migration show -1 for Z_MAX, whereas prior to migration they showed zero for empty tables and the maximum row number for populated tables. Manually updating Z_MAX to the proper values did not help with the exception. All Z_SUPER values were correct.
I set up a mapping model to see if anything looked awry with the automatic mappings, but everything looked fine.
Overall schema changes:
In the source version of the data model, there were fourteen entities, of which only four had been populated with data (the app is still in development). Seven were top-level entities and seven were sub-entities of three of the top-level entities.
In the target version of the data model, twenty-two entities were added, some top-level and some sub-entities, with dozens of relationships, including some added to existing entities.
Some attributes and relationships were removed from existing entities and others were added. No data types or relationship settings were changed, no attributes or relationships were renamed, and no special mappings were required.
Update (2/25/12): As I started working on a new intermediate model, I remembered that I had changed the class (representedClassName) for a number of entities from NSManagedObject to an NSManagedObject subclass, but hadn't generated the class files. I didn't suspect that would cause an issue and, indeed, creating all of the class files did not help with the exception. I just wanted to note that as another change between models.
Conclusions:
This is a wild guess, but if the 36 entity count is not a coincidence, it seems that when "myobject" attempts to fault in "object2" it does not have a valid reference for the table and is attempting to load table number -1, causing the exception. The fact that a simple assignment of [self object2] is successful, however, doesn't jibe with that conclusion.
Any ideas?
By working through several incremental migrations I was able to determine what is causing the issue, and a solution.
The problem:
One of the existing entities with data has no child entities in the current model. If I create a new model that simply adds a child entity, containing no attributes or relationships, and makes no other changes, the NSRangeException, Z_MAX observation, and doubling of the inverse relationship noted in my question all occur.
The solution:
After observing the failures following a "successful" lightweight migration for the case above, I created a mapping model. Since the only change was one additional entity, all but one of the entity mappings were straightforward. The question was what to do with the single added entity.
By default, the added entity with no attributes or relationships of its own was showing attribute and relationship mappings for all of the parent's properties. All of the mappings had empty value expressions by default, which I assumed meant that it would just skip them during the migration. Not true, apparently. By deleting all of the attribute and relationship mappings within the entity mapping and then turning off inferred mapping, the migration proceeded successfully.
I still have to tackle all of the remaining entities and will be trying this approach to do the rest in bulk, with all planned attributes and relationships intact.
Your posts were helpful when I encountered this problem. Thank you. [Have you reported the bug yet?]
Here are some more experimental results but, alas, not a great solution.
My schema change similarly added an entity subtype that has no additional attributes or relationships. The error message is the same as yours except the bounds are [0 .. 19]. That does correspond to 20 entity types, validating your hypothesis. Like your situation, the error happened when attempting to access an entity property after migration completed.
Adding a dummy attribute and a dummy self-relationship to the new entity type didn't avoid the post-migration crash. (However, I didn't test with that new entity type as the only schema change since I previously pushed that schema change to alpha testers.)
I observe the Z2_MYOBJECT column and Z_PRIMARYKEY.Z_MAX = -1 symptoms after successful migrations for other schema changes, so those may not be problematic at all. The -1 values get replaced lazily by the proper max values. The extra column might be used during migration.
In my case, the new entity's supertype has an ordered to-many relationship. In the very simple case where the entire data store contains just one object instance (an instance of that entity type with no outgoing relationship links), the schema migration succeeds. It does have the extra Z2_MYOBJECT column and Z_PRIMARYKEY.Z_MAX = -1 values and yet the resulting data store works fine when adding objects from there.
I tried creating a mapping model but was unsuccessful in getting Core Data to apply it. Turning off inferred mapping just made Core Data unable to migrate at all. Is there a trick to it? Do I have to write custom migration code to invoke a mapping model? This is Xcode 4.6.2 so the older bug is long gone.
When using git to roll the code & data model backwards or forwards to conduct an experiment, it seems to be necessary to (1) close & reopen the Xcode project and (2) do a clean build. Otherwise Xcode may crash and/or leave confounding state around.
To experimentally roll backwards, you must delete the .momd/ directory or the entire app from the target iOS simulator/device (or deploy the app via iTunes or TestFlight) since redeploying via Xcode won't remove obsolete files (like .mom and .omo data model definitions) which in turn lets the app do lightweight migrations that the actual deployed app can't do.
About the entity mapping to use for the added entity type, note that when Core Data applies a mapping model, it's copying entities from the old data store to a new one. It's not modifying the tables in place. You don't want it to "skip" properties (including inherited properties) unless you want to drop them.
However, since the schema change added an entity type, that entity has no instances to migrate so its custom mapping model rules do not matter.
Thus I wonder if something else caused your crashes to stop, like leftover experimental .mom files or custom migration code. Did your workaround hold up?
After 2 days of experimenting I decided my alpha testers would have to live without data migration this time. Fortunately this happened without production customers. But it doesn't give me confidence in Core Data.
I had the same sort of NSRangeException after adding a core data model version when accessing any instance of a particular entity after automatic lightweight migration. In my case also the range corresponded to the number of entities in my model.
I generated a mapping model with Xcode 4.6 (4H127) using File > New > File... and then selecting Core Data > Mapping Model. This caused the crash to (d)evolve into -[NSSymbolicExpression length]: unrecognized selector sent to instance...
Solution
The issue in my case was that my entity causing the original crash had a relationship named size, which is a reserved word listed in apple's Predicate Programming Guide. An examination of the mapping model revealed that the reserved word had been capitalized in the Value Expression for the relationship:
FUNCTION($manager, "destinationInstancesForEntityMappingNamed:sourceInstances:" , "PNSizeOptionToPNSizeOption", $source.SIZE)
I found the solution in Core Data Model Versioning and Data Migration Programming Guide:
Reserved words in custom value expressions: If you use a custom value
expression, you must escape reserved words such as SIZE, FIRST, and
LAST using a # (for example, $source.#size).
Unfortunately, Xcode's algorithm for generating the mapping model did not recognize the reserved word and I had to change the expression's key path in the Relationship Mapping inspector to $source.#size. This solved the problem. I assume that core data's inferred mapping model ran into a similar problem during lightweight migration.
There may be other causes of this kind crash and so this solution may not apply, but it may be worth checking the property names in your model against the list of reserved words in the Predicate Programming Guide.
So I am following the instructions found here: http://msdn.microsoft.com/en-US/data/jj691402 concerning how to handle multiple result sets from in EF.
I am trying to avoid the second solution as this will involve changing the EDMX by hand, which concerns me as I do not want to have to worry about other members on my team overwriting them.
But the first example still seems to be lacking. It refers to the ObjectContext.Translate<TEntity> method, but no where does it say how the <TEntity> is being created. Any time I create an Entity by hand, I of course get Error 2062, "no mapping between entity set and association set". Is there a step that I am missing? Or does the first solution not work with a DB first approach?
If you have create entity by hand in EF designer without mapping it to existing table or database view you indeed receive an error. Try to create complex type instead.
I'm pretty new to CakePHP and was missing a crucial feature not generated as scaffold: filtering.
What do I have to do to provide dropdowns or multi-selects on the index pages for each field that is a (foreign) key, thereby allowing to filter the table ("OR" inside multi-select, "AND" between different multi-selects, if any)?
From what my websearch has shown me there are many more people trying to accomplish the same thing, although I couldn't find anything that would work for me because either they have text fields and do wildcard filtering, or the plugins they propose only work for 1.2 whereas i now started with 1.3 etc. etc.
Can someone alleviate the confusion and maybe present some working code or direct me to the definitive guide[tm] where this matter has been solved?
Thx
It seems to me that scaffolding is provided as-is. If you find any helper accomplishing this, many would be interested, I'm sure. But scaffolding is not really meant satisfy such "complex" requirements, it just lists the row in the model.
Although it shouldn't be difficult to program what you want: using cake from the console it can generate you all the code that scaffold does, you only have to add your filters.
I think you want this one. The author of the filter wrote:
Filters hasOne and belongsTo relationships (I prefer selects from dropdowns, but to each their own).
I'm evaluating SubSonic 3.0 for use in our business as a replacement for our POCO objects. I'm new to SubSonic, literally installing it yesterday. I've gotten to the point where I can connect to one database using the 3.0 LINQ T4 Templates, and have been wooed by the promise of being able to connect to multiple databases in one application using SubSonic.
My issue is I can't find any documentation on how to use the T4 Templates with multiple databases (e.g. adding another connection string, setting up the Settings.ttinclude etc).
I've searched Google and Stackoverflow for an answer to see how this would be done or if its even possible. Any help would be appreciated.
So I seemed to be able to make it work by adding another connectionString to the web.config, and then adding a 2nd set of templates for that connectionString, it works, but it doesn't seem 'clean' or even really that DRY to me.
It also seems that I could do almost the same thing with the .NET Built in LINQ by adding multiple .dbml files.
Can anyone give me some reasoning at this point why we shouldn't just use the built in LINQ support over a 3rd party ORM like SubSonic?
Cross posting from the subsonic mailing list:
Oh yeah I do this all the time, the trick is two copies of the templates(easy) or editing the templates to iterate over two sets of tables(harder). In the second settings.tt change the name of the connection string to reflect the other database. You might also want to change the namespace so that you don't have conflicts where table names are the same. It seems hacky but I don't think it is because it allows you to make changes to the templates for each database independently.
If you really want only one set of templates the easiest way to go about it is to edit SQLServer.tt (or your choice of database) and override how LoadTables works such that it will accept a list of connections rather than a single one. I have to say this is a pain and it is going to be much harder than having 2 copies of the files.
(In reply to your answer of your question)
Can anyone give me some reasoning at this point why I shouldn't just use the built in LINQ over a 3rd party ORM like SubSonic?
On immediate thought: SubSonic supports more than just Microsoft Sql Server.
I have certain objects in my domain which are not aggregate roots/entities, yet I still need to retrieve them from a database. I don't want to confuse things by creating repositories for these things. So, what are alternative data access patterns? Would you simply create a DAO for them, while still of course separating the interface?
Edit:
Some more detail on what I'm doing. I need to create a code. This code has certain rules as to its format. One of the rules is that the final character must be a unique number incremented by one from the last code generated. For example:
ABCD1
ABCD2
ABCD3
So, I'm keeping a table with one row, one column to store the number in question. Now, I don't want to consider this number an entity and create a repository for it - that's overkill. I just need a way of retrieving the number, adding 1 to it, and saving it. I know there are myriad ways I could do it, but I'm wondering if there's an customary way.
There are several data access patterns that could apply, in theory. You'd need to provide more detail though if you want us to suggest a specific pattern.
Without more detail, all I can suggest is to consider looking into Martin Fowler's Patterns of Enterprise Application Architecture book.
Edit: Customary way? No, not that I can think of - it really depends on where and how you're using this unique code in your domain. If I were doing this, I'd probably create a small service that speaks directly to the database to perform this function - not as heavy-weight as a repository, and very focused on the problem at hand.
Based on the edit: I would look first at the context in which you need to create that code. Perhaps there are some related entities or something that you are missing.
btw, I find the question really interesting as it comes up from time to time while coding specific features. I usually end up finding I was missing something on the scenario and it ends up fitting well with the normal repository pattern.
After surveying the options I'm going with the Table Gateway pattern.