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POCore Data Lightweight Migration failure - "table ZTABLENAME already exists"
 

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  1. POCore Data Lightweight Migration failure - "table ZTABLENAME already exists"
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    <p>NB! I have seen <a href="https://stackoverflow.com/questions/9897452/core-data-migration-table-already-exists">Core Data Migration - Table Already Exists</a>, and it did not solve my problem.</p> <p>I'm trying to do a lightweight migration of my data model, and am getting a failure at this point:</p> <pre><code>NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil]; store = [self addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:url options:options error:&amp;error]; </code></pre> <p>The error message is:</p> <pre><code>2012-09-06 17:14:19.450 Selene[79064:c07] CoreData: error: (1) I/O error for database at /Users/colin/Library/Application Support/iPhone Simulator/5.1/Applications/E1638F38-B13A-4728-91CD-CC380E761544/Library/Application Support/Selene/.Selene.sqlite.migrationdestination_41b5a6b5c6e848c462a8480cd24caef3. SQLite error code:1, 'table ZMEASUREMENT already exists' </code></pre> <p>The actual change to the data model is the addition of a single optional string column on a completely different table, ZCYCLE. So it makes no sense that it's complaining about ZMEASUREMENT.</p> <p>I've stepped through the core data instantiation, and the NSManagedObjectModel looks like it is loaded correctly (new version). The url is correct.</p> <p>I've tried making Clean in xcode, Reset Contents and Settings... in iOS Simulator, regenerate a version-1 sqlite file from scratch (using Core Data), and then try migration to version-2 again -- no dice. So it's not that my sqlite file is corrupt somehow.</p> <p>Is data model information stored anywhere else that my cleaning might have missed?</p> <p>Is there any other way to debug what's actually happening in the lightweight migration? I can't find any information other than the "table already exists" error quoted above, which doesn't make any sense to me. Whatever's going on inside addPersistentStoreWithType: is opaque to me.</p> <p>The only way I have found to get a migration to proceed is to rename the table Core Data is complaining about, ZMEASUREMENT, as part of the migration. This works for one(1) migration only, and then I have to rename the table again to do a second migration. I am really not ok with the idea of a table whose name has to change every time I alter my data model; surely Core Data is not this broken.</p> <p>EDIT: In case it helps, here's the list of attributes for table ZMEASUREMENT. Is any of this weird?</p> <pre><code>@property (nonatomic) int epochDay; // Integer32 indexed // time as number of seconds since local midnight, to avoid time zone and DST issues @property (nonatomic, strong) NSNumber *localTime; // Integer32 optional // stored in Kelvins, to force me to test temperature conversion code properly @property (nonatomic, strong) NSNumber *temperatureK; // Float optional @property (nonatomic) BOOL excludeTemperature; // Boolean default=NO @property (nonatomic, strong) NSNumber *fluidCode; // Integer16 optional @property (nonatomic, strong) NSNumber *openingCode; // Integer16 optional @property (nonatomic, strong) NSNumber *positionCode; // Integer16 optional @property (nonatomic, strong) NSNumber *textureCode; // Integer16 optional @property (nonatomic, strong) NSNumber *rateCode; // Integer16 optional @property (nonatomic, strong) NSNumber *heightCode; // Integer16 optional // try renaming the internal property to see if it helps lightweight migration @property (nonatomic, strong) NSString *commentDPL; // String optional @property (nonatomic, strong) NSString *comment; /* derived property (alias for commentDPL) */ @property (nonatomic, strong) NSSet *notes; // Optional to-many relationship to MeasurementNote </code></pre> <p>The only non-optional fields are epochDay and excludeTemperature.</p>
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    1. COTo clarify (because someone asked), I'm not planning more than one migration right now, but I have a long wishlist of features, and sort of expect to be adding bits to the data model for a while. So I want to be able to do a migration as no big deal -- certainly the impression I get from "Core Data Model Versioning and Data Migration Programming Guide" is that it's supposed to be straightforward, right?
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