realm commit write error - Can't commit a non-existing write transaction

Question

I am trying to add a record to a realm DB table.

I have a class Connection which represents a table I need in my DB and have created dynamic vars which are to represent the columns:

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")
    }
}

Then in my code I am trying to write and commit the write transaction like so:

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

try! self.realm.commitWrite()

When running this code, I am receiving the error:

Can't commit a non-existing write transaction

What am I missing? Do I need to have inits in my ConnectionState class? Before adding in the commitWrite, I was trying to view the db with realm browser. I found my device in xCode and chose to download the container but it was empty. Then I thought I needed to add in commitWrite

Answer 1

In your example you called commitWrite without having called beginWrite. You cannot commit a write transaction because you did not start one. Either start a write transaction or delete the commitWrite line.

1. Start transaction and commit it

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

2. Delete commitWrite

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

The Realm docs have two examples of adding data to the database.

1. Use the realm.write method

   // 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. Use realm.beginWrite() and realm.commitWrite() to start the write transaction and commit data to the database

   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)
}

This code is somewhat equivalent to (possibly with some additional error handling):

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

Which means you're trying to commit your writes twice.

Just change your code like this:

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

// try! self.realm.commitWrite()