v2 RC2 (#33)

* Add PostgreSQL back end (#30)
* Upgrade password storage (#32)
* Change podcast/episode storage for SQLite (#29)
* Move date/time handling to NodaTime (#31)

src/MyWebLog.Data/Utils.fs

@@ -5,6 +5,9 @@ module internal MyWebLog.Data.Utils
 open MyWebLog
 open MyWebLog.ViewModels
 
+/// The current database version
+let currentDbVersion = "v2-rc2"
+
 /// Create a category hierarchy from the given list of categories
 let rec orderByHierarchy (cats : Category list) parentId slugBase parentNames = seq {
     for cat in cats |> List.filter (fun c -> c.ParentId = parentId) do
@@ -20,3 +23,36 @@ let rec orderByHierarchy (cats : Category list) parentId slugBase parentNames =
         yield! orderByHierarchy cats (Some cat.Id) (Some fullSlug) ([ cat.Name ] |> List.append parentNames)
 }
 
+/// Get lists of items removed from and added to the given lists
+let diffLists<'T, 'U when 'U : equality> oldItems newItems (f : 'T -> 'U) =
+    let diff compList = fun item -> not (compList |> List.exists (fun other -> f item = f other))
+    List.filter (diff newItems) oldItems, List.filter (diff oldItems) newItems
+
+/// Find meta items added and removed
+let diffMetaItems (oldItems : MetaItem list) newItems =
+    diffLists oldItems newItems (fun item -> $"{item.Name}|{item.Value}")
+
+/// Find the permalinks added and removed
+let diffPermalinks oldLinks newLinks =
+    diffLists oldLinks newLinks Permalink.toString
+
+/// Find the revisions added and removed
+let diffRevisions oldRevs newRevs =
+    diffLists oldRevs newRevs (fun (rev : Revision) -> $"{rev.AsOf.ToUnixTimeTicks ()}|{MarkupText.toString rev.Text}")
+
+open MyWebLog.Converters
+open Newtonsoft.Json
+
+/// Serialize an object to JSON
+let serialize<'T> ser (item : 'T) =
+    JsonConvert.SerializeObject (item, Json.settings ser)
+
+/// Deserialize a JSON string 
+let deserialize<'T> (ser : JsonSerializer) value =
+    JsonConvert.DeserializeObject<'T> (value, Json.settings ser)
+
+open Microsoft.Extensions.Logging
+
+/// Log a migration step
+let logMigrationStep<'T> (log : ILogger<'T>) migration message =
+    log.LogInformation $"Migrating %s{migration}: %s{message}"