ios – Why copy db files with 0 bytes in SwiftUI programming?

Code:

import SQLite
import SwiftUI

class CoreDataViewModel: ObservableObject {
    private var db: Connection?
    @Published var allEntries: [String] = []
    @Published var searchResults: [String] = []

    init() {
        copyDatabaseIfNeeded()
        openDatabase()
        fetchAllEntries()
    }

    deinit {
        closeDatabase()
    }

    private func openDatabase() {
        do {
            let documentsURL = try FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: false)
            let finalDatabaseURL = documentsURL.appendingPathComponent("english_grammar_today.db")

            db = try Connection(finalDatabaseURL.path)
            print("Successfully opened connection to database at \(finalDatabaseURL)")
        } catch {
            print("Unable to open database. Verify that you copied the database file to the documents directory.")
        }
    }

    private func closeDatabase() {
        db = nil
        print("Successfully closed connection to database")
    }


    func searchInDatabase(for keyword: String) {
        guard !keyword.isEmpty else {
            // If the keyword is empty, show all entries
            searchResults = allEntries
            return
        }

        do {
            let query = "SELECT entry FROM dictionary WHERE entry LIKE ?"
            searchResults = try db?.prepare(query + " ?", ["%" + keyword + "%"]).map { $0[0] as? String ?? "" } ?? []
        } catch {
            print("Error searching in database: \(error)")
        }
    }

    func fetchAllEntries() {
        do {
            let query = "SELECT entry FROM dictionary"
            allEntries = try db?.prepare(query).map { $0[0] as? String ?? "" } ?? []
        } catch {
            print("Error fetching all entries: \(error)")
        }
    }

    func copyDatabaseIfNeeded() {
        // Move database file from bundle to documents folder

        let fileManager = FileManager.default

        guard let documentsUrl = fileManager.urls(for: .documentDirectory, in: .userDomainMask).first else { return }

        let finalDatabaseURL = documentsUrl.appendingPathComponent("english_grammar_today.db")

        do {
            if !fileManager.fileExists(atPath: finalDatabaseURL.path) {
                print("DB does not exist in documents folder")

                if let dbFilePathPath = Bundle.main.path(forResource: "english_grammar_today", ofType: "db") {
                    try fileManager.copyItem(atPath: dbFilePath, toPath: finalDatabaseURL.path)
                } else {
                    print("Uh oh - english_grammar_today.db is not in the app bundle")
                }
            } else {
                print("Database file found at path: \(finalDatabaseURL.path)")
            }
        } catch {
            print("Unable to copy foo.db: \(error)")
        }
    }

}

The path

**DB does not exist in documents folder**

**Uh oh - foo.db is not in the app bundle**

**Successfully opened connection to database at file:///Users/howiema/Library/Developer/CoreSimulator/Devices/E49EA14F-17E0-4F09-8235-2F7F5835095F/data/Containers/Data/Application/46FA47A0-B2DE-4A9C-9346-5DD2B01C6F97/Documents/english_grammar_today.db**

**Error fetching all entries: no such table: dictionary (code: 1)**

After I clicked to run the program, I realized that the table dictionary does not exist… And I dunno why…

Dictionary Table

The link is picture, Why the db file is 0 byte??

/Users/howiema/Library/Developer/CoreSimulator/Devices/E49EA14F-17E0-4F09-8235-2F7F5835095F/data/Containers/Data/Application/46FA47A0-B2DE-4A9C-9346-5DD2B01C6F97/Documents/english_grammar_today.db

I want to copy the db file to that device file path, containing the structure and data