如何禁用WAL日志模式

Question

监督办/

我在禁用日记模式方面有问题。

我的代码是：

static NSManagedObjectContext *managedObjectContext(){
static NSManagedObjectContext *context = nil;
if (context != nil) {
    return context;
}

NSString * const NSSQLitePragmasOption;

NSSQLitePragmasOption : @{ @"journal_mode" : @"DELETE" };

@autoreleasepool {
    context = [[NSManagedObjectContext alloc] init];
    
    NSPersistentStoreCoordinator *coordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:managedObjectModel()];
    [context setPersistentStoreCoordinator:coordinator];
    
    NSString *STORE_TYPE = NSSQLiteStoreType;

    NSString *path = @"ExerciseDB";
    NSURL *url = [NSURL fileURLWithPath:[path stringByAppendingPathExtension:@"sqlite"]];
 
    NSError *error;
    NSPersistentStore *newStore = [coordinator addPersistentStoreWithType:STORE_TYPE configuration:nil URL:url options:NSSQLitePragmasOption error:&error];
    
    if (newStore == nil) {
        NSLog(@"Store Configuration Failure %@", ([error localizedDescription] != nil) ? [error localizedDescription] : @"Unknown Error");
    }
}
return context;
}

如何禁用日记模式WAL。

谢谢

Answer 1

若要禁用WAL模式，请将journal_mode设置为删除

NSMutableDictionary *pragmaOptions = [NSMutableDictionary dictionary];
[pragmaOptions setObject:@"DELETE" forKey:@"journal_mode"];

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, pragmaOptions, NSSQLitePragmasOption, nil];
[_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:options error:&error]

Answer 2

来自苹果技术文档：技术问答QA1809

NSDictionary *options = @{NSSQLitePragmasOption:@{@"journal_mode":@"DELETE"}};
if (! [persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType
                                            configuration:nil
                                            URL:storeURL
                                            options:options
                                            error:&error]) {
    // error handling.
}

编辑2020：

SwiftUI + iOS 14 (Xcode 12 beta 6)

使用SwiftUI创建新项目并检查CoreData模板时，新项目的Persistence.swift文件中有以下代码：

struct PersistenceController {
    static let shared = PersistenceController()

    //...

    let container: NSPersistentContainer

    init(inMemory: Bool = false) {
        container = NSPersistentContainer(name: "db_name")
        if inMemory {
            container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
        }
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                //...
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
    }
}

现在，您可以在init容器(container = NSPersistentContainer(name: "db_name"))之后添加以下代码块

if let url = container.persistentStoreDescriptions.first?.url {
    let storeDescription = NSPersistentStoreDescription(url: url)
    storeDescription.setValue("DELETE" as NSObject, forPragmaNamed: "journal_mode")
    container.persistentStoreDescriptions = [storeDescription]
}

Answer 3

对于Swift 2，其内容如下：

    let dict: [NSObject : AnyObject] = [
        NSSQLitePragmasOption: ["journal_mode":"DELETE"]
    ]

    do {
        try coordinator.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: dict)
    } catch {
        // Report any error we got.
        var dict = [String: AnyObject]()
        dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
        dict[NSLocalizedFailureReasonErrorKey] = failureReason

        dict[NSUnderlyingErrorKey] = error as! NSError
        let wrappedError = NSError(domain: "YOUR_ERROR_DOMAIN", code: 9999, userInfo: dict)
        // Replace this with code to handle the error appropriately.
        // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
        NSLog("Unresolved error \(wrappedError), \(wrappedError.userInfo)")
        abort()
    }