set the DefaultDBType as the default database option in the Installer and Add Site UI

Oqtane.Client/Installer/Installer.razor

@@ -30,10 +30,17 @@
                                 @if (_databases != null)
                                 {
                                     foreach (var database in _databases)
+                                    {
+                                        if (database.IsDefault)
+                                        {
+                                            <option value="@database.Name" selected>@Localizer[@database.Name]</option>
+                                        }
+                                        else
                                         {
                                             <option value="@database.Name">@Localizer[@database.Name]</option>
                                         }
                                     }
+                                }
                             </select>
                         </td>
                     </tr>

Oqtane.Client/Modules/Admin/Sites/Add.razor

@@ -129,9 +129,16 @@ else
                 <td>
                     <select id="databaseType" class="custom-select" value="@_databaseName" @onchange="(e => DatabaseChanged(e))">
                         @foreach (var database in _databases)
+                        {
+                            if (database.IsDefault)
+                            {
+                                <option value="@database.Name" selected>@Localizer[@database.Name]</option>
+                            }
+                            else
                             {
                                 <option value="@database.Name">@Localizer[@database.Name]</option>
                             }
+                        }
                     </select>
                 </td>
             </tr>

Oqtane.Server/Controllers/DatabaseController.cs

@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Options;
+using Oqtane.Infrastructure;
 using Oqtane.Models;
 using Oqtane.Shared;
 
@@ -10,17 +11,25 @@ namespace Oqtane.Controllers
     public class DatabaseController : Controller
     {
         private IOptions<List<Database>> _databaseOptions;
+        private IConfigManager _config;
 
-        public DatabaseController(IOptions<List<Database>> databaseOptions)
+        public DatabaseController(IOptions<List<Database>> databaseOptions, IConfigManager config)
         {
             _databaseOptions = databaseOptions;
+            _config = config;
         }
 
         // GET: api/<controller>
         [HttpGet]
-        public IEnumerable<Models.Database> Get()
+        public IEnumerable<Database> Get()
         {
-            return _databaseOptions.Value;
+            var databases = _databaseOptions.Value;
+            var master = _config.GetSetting(SettingKeys.DatabaseSection, SettingKeys.DatabaseTypeKey, "");
+            if (master != "" && databases.Exists(item => item.DBType == master))
+            {
+                databases.Find(item => item.DBType == master).IsDefault = true;
+            }
+            return databases;
         }
     }
 }

Oqtane.Shared/Models/Database.cs

@@ -19,5 +19,10 @@ namespace Oqtane.Models
         /// Type of DB using the full namespace, like `Oqtane.Database.SqlServer.SqlServerDatabase, Oqtane.Database.SqlServer`
         /// </summary>
         public string DBType { get; set; }
+
+        /// <summary>
+        /// whether this item is the default database provider ( ie. specified by DefaultDBType in appsettings.json )
+        /// </summary>
+        public bool IsDefault { get; set; }
     }
 }