When you chat with a bot built with Azure Bot Service, you will have to maintain user state. Example, the options that the user chose last time, or the usernames of all users in a conversation.
Conversation State Types
Azure Bot Service has 3 different states:
User State
This state is related to the user on a specific channel regardless how many conversation they have. So, if the user is chatting with a bot from Facebook channel and connected to the same bot in another conversation , any values saved in user state will be visible in both chats. This is useful in scenarios where you want to save an info about the user like the username or preference that will be used in all conversation for this user.
Conversation State
This state is scoped to the conversation only but not to each user. If you have 3 users chatting with the bot, any data saved in conversation state will be shared across all users. This is used in cases where the data saved is not related to a specific user such as statistics. If the user connected to another session with the bot, the info saved her will not be visible in the other conversation
Private Conversation State
Here, the framework manages the state for each user in each conversation. Imagine a scenario where the user is submitting a ticket. You want the ticket info to be scoped to this conversation only because they may be submitting another ticket with another conversation.
The state storage saves each data in a key/value store. The keys used for each state type is as below:
- User Sate: {Activity.ChannelId}/users/{Activity.From.Id}#YourPropertyName
- Conversation state: {Activity.ChannelId}/conversations/{Activity.Conversation.Id}#YourPropertyName
- Private conversation: {Activity.ChannelId}/conversations/{Activity.Conversation.Id}/users/{Activity.From.Id}#YourPropertyName
Conversation Storage
By default, the state variables are stored in memory. But you can change that from the startup.cs. In the example below, I have configured it to use Azure Table storage to store the state, this makes it persistent. You can create your own state by inheriting from IStorage
Next, you configure which state types you want to use, in this example, I use the conversation state. To use the user state, you have to create an instance of UserState and add it as a singleton just like conversation state.
public void ConfigureServices(IServiceCollection services)
{
//IStorage dataStore = new MemoryStorage();
IStorage dataStore = new Microsoft.Bot.Builder.Azure.AzureBlobStorage("connection string", storageContainer);
var conversationState = new ConversationState(dataStore);
services.AddSingleton(conversationState);
}
State property accessors
Now, its time to use the state in our bot. To do that, you have to use a property accessor which allows you to read and update data to the state storage. Note that calling the GetAsync and SetAsync on the state accessor doesn’t actually save the state data in the storage system. You have to call the SaveChangesAsync as you can see from the sequence diagram above.
To understand more about state property accessors and how to use it to read and update data into bot state, go through this link
Haitham Shaddad Blog, Design and Build Web Applications with Azure and .Net 
