New ext methods to check if Umbraco db is installed, fixes issue with SqlMainDomLock when doing unattended installs, changes how we determine if Umbraco db is installed

src/Umbraco.Core/Persistence/UmbracoDatabaseExtensions.cs

@@ -1,4 +1,7 @@
 using System;
+using System.Linq;
+using Umbraco.Core.Logging;
+using Umbraco.Core.Migrations.Install;
 
 namespace Umbraco.Core.Persistence
 {
@@ -10,5 +13,57 @@ namespace Umbraco.Core.Persistence
             if (asDatabase == null) throw new Exception("oops: database.");
             return asDatabase;
         }
+
+        /// <summary>
+        /// Returns true if the database contains the specified table
+        /// </summary>
+        /// <param name="database"></param>
+        /// <param name="tableName"></param>
+        /// <returns></returns>
+        public static bool HasTable(this IUmbracoDatabase database, string tableName)
+        {
+            try
+            {
+                return database.SqlContext.SqlSyntax.GetTablesInSchema(database).Any(table => table.InvariantEquals(tableName));
+            }
+            catch (Exception)
+            {
+                return false; // will occur if the database cannot connect
+            }
+        }
+
+        /// <summary>
+        /// Returns true if the database contains no tables
+        /// </summary>
+        /// <param name="database"></param>
+        /// <returns></returns>
+        public static bool IsDatabaseEmpty(this IUmbracoDatabase database)
+            => database.SqlContext.SqlSyntax.GetTablesInSchema(database).Any() == false;
+
+        /// <summary>
+        /// Returns the <see cref="DatabaseSchemaResult"/> for the database
+        /// </summary>
+        /// <param name="database"></param>
+        /// <param name="logger"></param>
+        /// <returns></returns>
+        public static DatabaseSchemaResult ValidateSchema(this IUmbracoDatabase database, ILogger logger)
+        {
+            var dbSchema = new DatabaseSchemaCreator(database, logger);
+            var databaseSchemaValidationResult = dbSchema.ValidateSchema();            
+            return databaseSchemaValidationResult;
+        }
+
+        /// <summary>
+        /// Returns true if Umbraco database tables are detected to be installed
+        /// </summary>
+        /// <param name="database"></param>
+        /// <param name="logger"></param>
+        /// <returns></returns>
+        public static bool IsUmbracoInstalled(this IUmbracoDatabase database, ILogger logger)
+        {
+            var databaseSchemaValidationResult = database.ValidateSchema(logger);
+            return databaseSchemaValidationResult.DetermineHasInstalledVersion();
+        }
+
     }
 }