append to a json file in swift

To append data to a JSON file in Swift, you can follow these steps:

1. Create a Swift dictionary with the data you want to append to the JSON file.

   main.swift
   let newData = ["key": "value"]
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2. Open the JSON file for writing.

   main.swift
   guard let fileURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first?.appendingPathComponent("example.json") else {
       fatalError("Failed to get file URL")
   }
   
   var jsonData = try Data(contentsOf: fileURL)
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3. Decode the JSON data from the file into a Swift dictionary.

   main.swift
   var existingData: [String: Any] = [:]
   if !jsonData.isEmpty {
       existingData = try JSONSerialization.jsonObject(with: jsonData, options: []) as? [String: Any] ?? [:]
   }
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4. Merge the new data with the existing data to create a new dictionary.

   main.swift
   let mergedData = existingData.merging(newData, uniquingKeysWith: { (_, last) in last })
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5. Encode the merged data as JSON.

   main.swift
   jsonData = try JSONSerialization.data(withJSONObject: mergedData, options: [.prettyPrinted])
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6. Write the JSON data back to the file, appending to the end of the file.

   main.swift
   if let fileHandle = FileHandle(forWritingAtPath: fileURL.path) {
        defer {
            fileHandle.closeFile()
        }
        fileHandle.seekToEndOfFile()
        fileHandle.write(jsonData)
    } else {
        try jsonData.write(to: fileURL, options: .atomic)
    }
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The atomic option ensures that the file is written atomically, meaning that the data is first written to a temporary file and then moved to the original file. This ensures that the file is not corrupted if the write operation is interrupted.

Note: It's important to ensure that the file you're writing to is a valid JSON file, otherwise the JSON decoding/encoding operations will fail.