领域提交写入错误 - 无法提交不存在的写入事务

Question

我正在尝试向领域数据库表中添加一条记录。

我有一个连接类，它代表我在数据库中需要的一个表，并创建了动态变量来代表列：

import Foundation
import RealmSwift
import Realm

open class ConnectionState: Object {

    open dynamic var _id : String = NSUUID().uuidString
    open dynamic var a : String = ""
    open dynamic var b : String = ""
    open dynamic var c : Int = 0

    open override class func primaryKey() -> String? {
        return "_id"
    }

    required public init() {
        super.init()
    }

    required public init(realm: RLMRealm, schema: RLMObjectSchema) {
        super.init(realm: realm, schema: schema)
    }

    required public init(value: Any, schema: RLMSchema) {
        fatalError("init(value:schema:) has not been implemented")
    }
}

然后在我的代码中，我尝试像这样编写并提交写入事务：

let ConnectionState = ConnectionState()
ConnectionState.a = "a"
ConnectionState.b = "b"
ConnectionState.c = 1
try! self.realm.write {
     self.realm.add(ConnectionState)
}

try! self.realm.commitWrite()

运行此代码时，我收到错误消息：

Can't commit a non-existing write transaction

我错过了什么？我的 ConnectionState 类中是否需要初始化？ 在添加 commitWrite 之前，我试图用领域浏览器查看数据库。我在 xCode 中找到了我的设备并选择下载容器，但它是空的。然后我想我需要添加commitWrite

Answer 1

在您的示例中，您调用了commitWrite 而没有调用beginWrite。你不能提交一个写事务，因为你没有启动一个。启动写入事务或删除 commitWrite 行。

1. 启动事务并提交

   self.realm.beginWrite()
   
   self.realm.add(ConnectionState)
   
   try! self.realm.commitWrite()
   

2. 删除提交写入

   try! self.realm.write {
        self.realm.add(ConnectionState)
   }
   

Realm docs 有两个向数据库添加数据的示例。

1. 使用realm.write 方法

   // Use them like regular Swift objects
   let myDog = Dog()
   myDog.name = "Rex"
   myDog.age = 1
   print("name of dog: \(myDog.name)")
   
   // Get the default Realm
   let realm = try! Realm()
   
   // Query Realm for all dogs less than 2 years old
   let puppies = realm.objects(Dog.self).filter("age < 2")
   puppies.count // => 0 because no dogs have been added to the Realm yet
   
   // Persist your data easily
   try! realm.write {
       realm.add(myDog)
   }
   

2. 使用realm.beginWrite()和realm.commitWrite()启动写事务并将数据提交到数据库

   let realm = try! Realm()
   
   // Break up the writing blocks into smaller portions
   // by starting a new transaction
   for idx1 in 0..<1000 {
     realm.beginWrite()
   
     // Add row via dictionary. Property order is ignored.
     for idx2 in 0..<1000 {
       realm.create(Person.self, value: [
         "name": "\(idx1)",
         "birthdate": Date(timeIntervalSince1970: TimeInterval(idx2))
       ])
     }
   
     // Commit the write transaction
     // to make this data available to other threads
     try! realm.commitWrite()
   }
   

Answer 2

try! self.realm.write {
     self.realm.add(ConnectionState)
}

这段代码有点等价于（可能带有一些额外的错误处理）：

realm.beginWrite()
...
try! realm.commitWrite()

这意味着您尝试提交两次写入。

只需像这样更改您的代码：

try! self.realm.write {
     self.realm.add(ConnectionState)
}

// try! self.realm.commitWrite()