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[PersistedClass]
public class User : DataItem
{
    [PersistedProperty(IdOrder = 1)]
    public string Username { get => getter<string>(); set => setter(value); }

    [PersistedProperty]
    public DateTime LastLoginTime { get => getter<DateTime>(); set => setter(value); }

    [PersistedProperty(ReverseRef = nameof(ChatMessage.Author))]
    public DataItemRefList<ChatMessage> Messages => getList<ChatMessage>();

    [PersistedProperty(ReverseRef = nameof(ChatRoom.Users))]
    public DataItemRefList<ChatRoom> ChatRooms => getList<ChatRoom>();
}

[PersistedClass]
public class ChatRoom : DataItem
{
    [PersistedProperty(IdOrder = 1, AutoValue = AutoValue.Identity)]
    public long Id { get => getter<long>(); set => setter(value); }

    [PersistedProperty(IsMandatory = true)]
    public string Name { get => getter<string>(); set => setter(value); }

    [PersistedProperty]
    public DataItemRefList<ChatMessage> Messages => getList<ChatMessage>();

    [PersistedProperty(ReverseRef = nameof(User.ChatRooms))]
    public DataItemRefList<User> Users => getList<User>();
}

[PersistedClass]
public class ChatMessage : DataItem
{
    [PersistedProperty(IdOrder = 1, AutoValue = AutoValue.Identity)]
    public long Id { get => getter<long>(); set => setter(value); }

    [PersistedProperty]
    public string Text { get => getter<string>(); set => setter(value); }

    [PersistedProperty]
    public DateTime CreatedTime { get => getter<DateTime>(); set => setter(value); }

    [PersistedProperty]
    public DateTime FirstReadTime { get => getter<DateTime>(); set => setter(value); }

    [PersistedProperty(ReverseRef = nameof(User.Messages))]
    public User Author { get => getter<User>(); set => setter(value); }
}

// Reading a user
var key = DataItemKey.BuildKey<User>("myusername");
var user = client.ReadDataItem<User>(key);

// Reading a chatroom
var key = DataItem.BuildKey<ChatRoom>(1);
var room = client.ReadDataItem<ChatRoom>(key);

// updating user scalar value
user.LastLoginTime = DateTime.Now;
client.Save(user);

// creating a message
var msg = client.CreateDataItem<Message>();
msg.Text = "Hello my friend";
msg.User = user; // creating a relation between msg and user, back reference is automatically assigned
msg.Room = room; // creating a relation between msg and chat room, back reference is automatically assigned
client.Save(msg, room, user);

// Deleting a user
user.MarkForDeletion();
client.Save(user);

// Reading a user
var key = DataItem.BuildKey<User>("myusername");
var user = client.ReadDataItem<User>(key);

// Reading a chatroom
var key = DataItem.BuildKey<ChatRoom>(1);
var room = client.ReadDataItem<ChatRoom>(key);

// Subscribe to all transaction events
client.DataItemSaved += (o, e) => Console.WriteLine(
  $"Changed Item: {e.DataItem.FullId}," + Environment.NewLine +
  $"Changed Fields: { String.Join(',', e.GetChangedFields().Keys)}"); 

// Subscribe to all transaction change events that that occur at every instance and the client listens to
client.DataItemSaved += (o, e) => Console.WriteLine(
  $"Changed Item: {e.DataItem.FullId}," + Environment.NewLine +
  $"Changed Fields: { String.Join(',', e.GetChangedFields().Keys)}"); 

// Subscribe to transaction change events that occur at every instance of a specific type, eg chatrooms
var roomClassInfo = DataItem.GetClassInfo(typeof(ChatRoom));
roomClassInfo.DataItemSaved += (o, e) => Console.WriteLine(
  $"Changed Item: {e.DataItem.FullId}," + Environment.NewLine +
  $"Changed Fields: { String.Join(',', e.GetChangedFields().Keys)}"); 

// Subscribe to transaction change events for the specific instance, eg chatroom 1
room.DataItemSaved += (o, e) => Console.WriteLine(
  $"Changed Item: {e.DataItem.FullId}," + Environment.NewLine +
  $"Changed Fields: { String.Join(',', e.GetChangedFields().Keys)}"); 

// Subscribe to transaction change events that occur to references of the specific instance
room.DataItemReferenceSaved += (o, e) => Console.WriteLine(
  $"Changed Item: {e.DataItem.FullId}," + Environment.NewLine +
  $"Changed Fields: { String.Join(',', e.GetChangedFields().Keys)}"); 

// Subsribe to all instance changes, both transaction and local changes
client.DataItemChanged += (o, e) => Console.WriteLine(
  $"Changed Item: {e.DataItem.FullId}," + Environment.NewLine +
  $"Changed Fields: {String.Join(',', e.ChangedPropertyNames)}");

// Subsribe to standard .NET property change events, both transaction and local changes
user.PropertyChanged += (o, e) => Console.WriteLine( e.PropertyName );

// get Message class info
var msgClassInfo = DataItem.GetClassInfo(typeof(Message));

/********  perform query using the simple syntax ********/

// create expression
var expr = new ExpressionBuilder($"where {nameof(Message.IsRead)} = true");
expr.DeclareClassInfo(msgClassInfo);

// create where expression
var whereIsReadExpr = expr.Create(msgClassInfo);

// create query (validator)
var validator = new DataItemCollectionValidator<Message>(true) as IDataItemCollectionValidator<Message>;
validator.QueryExpression = whereActiveExpr;
validator.IsForceLoader = true;

// read current instances and create a collection that is automatically validated against the query and updated on each transaction
client.ReadDataItems(validator);


/******** perform query uisng the verbose syntax ********/

// get IsRead field
var isReadField = msgClassInfo.GetField(nameof(Message.IsRead));

// create where expression
var whereIsReadExpr = new WhereComparisonExpression(isReadField, WhereOperator.Equal, false);

// create query (validator)
var validator = new DataItemCollectionValidator<Message>(true) as IDataItemCollectionValidator<Message>;
validator.QueryExpression = whereActiveExpr;
validator.IsForceLoader = true;

// read instances based on query (non-live collection)
client.ReadDataItems(validator);

/******** Query based Live Collection ********/

// create expression
var expr = new ExpressionBuilder($"where {nameof(Message.IsRead)} = true");
expr.DeclareClassInfo(msgClassInfo);

// create where expression
var whereIsReadExpr = expr.Create(msgClassInfo);

// create query (validator)
var validator = new DataItemCollectionValidator<Message>(true) as IDataItemCollectionValidator<Message>;
validator.QueryExpression = whereActiveExpr;
validator.IsForceLoader = true;

// read current instances and create a collection that is automatically validated against the query
var liveCollection = client.ReadDataCollection(validator);

// subscribe to transactions changes. Track additions and removals in the list
liveCollection.DataItemListSaved += (o, e) => Console.Write(
  $"Added Members:" + String.Join(',', e.AddedMembers.Select(x => x.FullId)) + Environment.NewLine +
  $"Removed Members:" + String.Join(',', e.RemovedMembers.Select(x => x.FullId)));

// Subscribe to transaction change events that occur to a reference list members
liveCollection.DataItemListMemberSaved += (o, e) => Console.WriteLine(
  $"Changed Item: {e.DataItem.FullId}," + Environment.NewLine +
  $"Changed Fields: { String.Join(',', e.GetChangedFields().Keys)}"); 


/******** Reference List Live Collection ********/

// subscribe to transactions changes. Track additions and removals in the list
room.Messages.DataItemListSaved += (o, e) => Console.Write(
  $"Added Members:" + String.Join(',', e.AddedMembers.Select(x => x.FullId)) + Environment.NewLine +
  $"Removed Members:" + String.Join(',', e.RemovedMembers.Select(x => x.FullId)));

// Subscribe to transaction change events that occur to a reference list members
room.Messages.DataItemListMemberSaved += (o, e) => Console.WriteLine(
  $"Changed Item: {e.DataItem.FullId}," + Environment.NewLine +
  $"Changed Fields: { String.Join(',', e.GetChangedFields().Keys)}");