feature: Add function to set journal mode on sqlite databases (apollo…

…graphql/apollo-ios-dev#443)

Sources/ApolloSQLite/JournalMode.swift

@@ -0,0 +1,20 @@
+import Foundation
+
+public enum JournalMode: String {
+  /// The rollback journal is deleted at the conclusion of each transaction. This is the default behaviour.
+  case delete = "DELETE"
+  /// Commits transactions by truncating the rollback journal to zero-length instead of deleting it.
+  case truncate = "TRUNCATE"
+  /// Prevents the rollback journal from being deleted at the end of each transaction. Instead, the header
+  /// of the journal is overwritten with zeros.
+  case persist = "PERSIST"
+  /// Stores the rollback journal in volatile RAM. This saves disk I/O but at the expense of database
+  /// safety and integrity.
+  case memory = "MEMORY"
+  /// Uses a write-ahead log instead of a rollback journal to implement transactions. The WAL journaling
+  /// mode is persistent; after being set it stays in effect across multiple database connections and after
+  /// closing and reopening the database.
+  case wal = "WAL"
+  /// Disables the rollback journal completely
+  case off = "OFF"
+}

Sources/ApolloSQLite/SQLiteDatabase.swift

@@ -9,7 +9,7 @@ public struct DatabaseRow {
 }
 
 public protocol SQLiteDatabase {
-  
+
   init(fileURL: URL) throws
 
   func createRecordsTableIfNeeded() throws
@@ -23,7 +23,7 @@ public protocol SQLiteDatabase {
   func deleteRecords(matching pattern: CacheKey) throws
 
   func clearDatabase(shouldVacuumOnClear: Bool) throws
-  
+
 }
 
 public extension SQLiteDatabase {

Sources/ApolloSQLite/SQLiteDotSwiftDatabase.swift

@@ -10,7 +10,7 @@ public final class SQLiteDotSwiftDatabase: SQLiteDatabase {
   private let records: Table
   private let keyColumn: SQLite.Expression<CacheKey>
   private let recordColumn: SQLite.Expression<String>
-  
+
   public init(fileURL: URL) throws {
     self.records = Table(Self.tableName)
     self.keyColumn = Expression<CacheKey>(Self.keyColumnName)
@@ -66,4 +66,11 @@ public final class SQLiteDotSwiftDatabase: SQLiteDatabase {
       try self.db.prepare("VACUUM;").run()
     }
   }
+
+  /// Sets the journal mode for the current database.
+  ///
+  /// - Parameter mode: The journal mode controls how the journal file is stored and processed.
+  public func setJournalMode(mode: JournalMode) throws {
+    try self.db.run("PRAGMA journal_mode = \(mode.rawValue)")
+  }
 }