#3 Oracle sequence implementation of HiLoIdGenerator added

src/Backend.Fx.EfCorePersistence/OracleSequenceHiLoIdGenerator.cs

@@ -0,0 +1,65 @@
+namespace Backend.Fx.EfCorePersistence
+{
+    using System;
+    using System.Data.Common;
+    using Backend.Fx.Logging;
+    using Backend.Fx.Patterns.IdGeneration;
+    using Microsoft.EntityFrameworkCore;
+
+    public abstract class OracleSequenceHiLoIdGenerator : HiLoIdGenerator
+    {
+        private static readonly ILogger Logger = LogManager.Create<OracleSequenceHiLoIdGenerator>();
+        private readonly DbContextOptions dbContextOptions;
+        private readonly string sequenceName;
+
+        protected OracleSequenceHiLoIdGenerator(DbContextOptions dbContextOptions, string sequenceName)
+        {
+            this.dbContextOptions = dbContextOptions;
+            this.sequenceName = sequenceName.ToUpperInvariant();
+        }
+
+        protected override int GetNextBlockStart()
+        {
+            using (DbContext dbContext = new DbContext(dbContextOptions))
+            {
+                using (DbConnection dbConnection = dbContext.Database.GetDbConnection())
+                {
+                    dbConnection.Open();
+                    int nextBlockStart;
+                    using (DbCommand command = dbConnection.CreateCommand())
+                    {
+                        command.CommandText = $"SELECT {sequenceName}.NEXTVAL FROM dual";
+                        nextBlockStart = Convert.ToInt32(command.ExecuteScalar());
+                        Logger.Debug($"{sequenceName} served {nextBlockStart} as next value");
+                    }
+                    return nextBlockStart;
+                }
+            }
+        }
+
+        public void EnsureSqlSequenceExistence()
+        {
+            using (DbContext dbContext = new DbContext(dbContextOptions))
+            {
+                using (DbConnection dbConnection = dbContext.Database.GetDbConnection())
+                {
+                    dbConnection.Open();
+                    bool sequenceExists;
+                    using (DbCommand command = dbConnection.CreateCommand())
+                    {
+                        command.CommandText = $"SELECT count(*) FROM user_sequences WHERE sequence_name = '{sequenceName}'";
+                        sequenceExists = (decimal)command.ExecuteScalar() == 1;
+                    }
+                    if (!sequenceExists)
+                    {
+                        using (DbCommand command = dbConnection.CreateCommand())
+                        {
+                            command.CommandText = $"CREATE SEQUENCE {sequenceName} START WITH 1 INCREMENT BY {Increment}";
+                            command.ExecuteNonQuery();
+                        }
+                    }
+                }
+            }
+        }
+    }
+}