Data play an important part in our project,how can we ensure correctness of the data and prevent the data
from error.In relational database, we are famillar with the usage of transaction.
beginopreationscommit/rollback
But there are some differences between the Redis and relational database.Let's introduce the commands
first.There are only 5 commands to use while you use the transaction in redis.
I want to take an example to show you how to use the transaction.So here is the backgroud.There are three
persons and they want to buy the apple from the shop.The key for buying apple is the amount.
For this example,I use the hash to store the infomation of the users and the products.I use the string to store
the totalmoney for the trade.The following picture shows this example's initial data.
Let's start to finish this example.The first step is to initialize the data.
hmset user-1 name tom money 200hmset user-2 name jack money 300hmset user-3 name paul money 500hmset product-1 name apple price 150 amount 2set totalmoney 0
Tom wants to buy the apple,so the product-1's amount should decrease by one,tom's money should decrease
by 150 and the totalmoney should increase by 150.The action buy includes three steps.We should check up the
product-1 with buy action.
watch product-1multihincrby product-1 amount -1hincrby user-1 money -150incrby totalmoney 150exec
You will find that after the command multi ,the commands before exec all return queued.It means that those
commands store in a queue.After exec command,the client send this queue to the server and execute the commands.
But this is a normal situation that the amount is not changed before the transaction execute.
this,we need another client to imitate paul takes first.Before execute the transaction of jack's action,we decrease the
amount of product-1 to imitate paul buy the apple first.After executing the transaction of jack's action,the client returns
(nil) meaning the transaction of jack's action executed fail and the three commands didn't execute too.
This example shows the basic usage of transaction in redis.It is suitable for many questions.
execute the command exec will return an error.Because the multi didn't exists in this session.
Now I will show you how to use the transaction in StackExchange.Redis.
1 //Initiate the data 2 db.HashSet("user-1", new HashEntry[2] { new HashEntry("name", "tom"), new HashEntry("money", 200) }); 3 db.HashSet("user-2", new HashEntry[2] { new HashEntry("name", "jack"), new HashEntry("money", 300) }); 4 db.HashSet("user-3", new HashEntry[2] { new HashEntry("name", "paul"), new HashEntry("money", 500) }); 5 db.HashSet("product-1", new HashEntry[3] { new HashEntry("name", "apple"), new HashEntry("price", 150),new HashEntry("amount", 2) }); 6 db.StringSet("totalmoney", 0); 7 8 //multi 9 var tran = db.CreateTransaction();10 //watch11 tran.AddCondition(Condition.HashEqual("product-1", "amount", "2"));12 13 tran.HashDecrementAsync("product-1", "amount");14 tran.HashDecrementAsync("user-1", "money", 150);15 tran.StringIncrementAsync("totalmoney", 150);16 17 Console.WriteLine(string.Format("execute the transaction {0}!", tran.Execute() ? "Y" : "N"));18 19 //multi20 var tran2 = db.CreateTransaction();21 //watch22 tran.AddCondition(Condition.HashEqual("product-1", "amount", "1"));23 24 tran.HashDecrementAsync("product-1", "amount");25 tran.HashDecrementAsync("user-2", "money", 150);26 tran.StringIncrementAsync("totalmoney", 150);27 28 //paul take first29 db.HashDecrement("product-1", "amount");30 31 Console.WriteLine(string.Format("execute the transaction {0}!", tran.Execute() ? "Y" : "N"));
Debuging the code ,you will see the result as follow.
