I have a sequence of messages need to be converted and saved into database. Messages come out of order and I want to make sure only the latest message is saved into database. Each message has a timestamp.
Say the message is like
{
personId: string
value: string
timeStampe: BigInteger
}
The database schema be like
personId: string | content : string | timestamp: BigInteger
So it's an upsert with condition:
if `personId` not exists in database, `INSERT` the record,
else if `personId` exists and incoming timestamp > timestamp in database, `UPDATE` the record.
else do nothing
for update I can do a find then update, just want to know if there's anyway to do it in one call (something already defined by SpringData JPA?). The database is DB2.
Thanks
Related
I am trying to retrieve data in my MongoDB database. If I have the following below in my mongoDB database, I want to select the Password given the Username. So in this case, I will be looking through the database for a Username that is 'e' and retrieving the password associated with that specific Username. I've tried looking everywhere but I can't seem to find a solution on how to do it. I am using express, node, and mongoDB for this personal project. What I have so far is just looking up with database with .find({ Username: Username} and it outputs the entire JSON object.
To clarify, I will be sending a request with a Username of value 'e' and looking it up the database trying to retrieve the value of Password.
{
_id: 62d7712e6d6732706b46094e,
Username: 'e',
Password: 'hi',
__v: 0
}
find takes multiple inputs you can give the select statements also in find itself
so the query will be like
db.collectionName.find({username:'e'},{_id:0,password:1})
mongo by default fetch _id all the time by default so you need to specifically mention to not fetch _id thus _id :0
for such scenarios, there are 2 options if username is unique i would suggest to go with findOne rather then find
db.collectionName.findOne({username:'e'}).password
the same will work if you have multiple records with same username but you want only the first record
but if you want data of all the records as array
db.collectionName.find({username:'e'},{_id:0,password:1})..map( function(u) { return u.password; } )
I have a custom object consent and preferences which is child to account.
Requirement is to restrict duplicate record based on channel field.
foe example if i have created a consent of channel email it should throw error when i try to create second record with same email as channel.
The below is the code i have written,but it is letting me create only one record .for the second record irrespective of the channel its throwing me the error:
Trigger code:
set<string> newChannelSet = new set<string>();
set<string> dbChannelSet = new set<string>();
for(PE_ConsentPreferences__c newCon : trigger.new){
newChannelSet.add(newCon.PE_Channel__c);
}
for(PE_ConsentPreferences__c dbcon : [select id, PE_Channel__c from PE_ConsentPreferences__c where PE_Channel__c IN: newChannelSet]){
dbChannelSet.add(dbcon.PE_Channel__c);
}
for(PE_ConsentPreferences__c newConsent : trigger.new){
if(dbChannelSet.contains(newConsent.PE_Channel__c))
newConsent.addError('You are inserting Duplicate record');
}
Your trigger blocks you because you didn't filter by Account in the query. So it'll let you add 1 record of each channel type and that's all.
I recommend not doing it with code. It is going to get crazier than you think really fast.
You need to stop inserts. To do that you need to compare against values already in the database (fine) but also you should protect against mass loading with Data Loader for example. So you need to compare against other records in trigger.new. You can kind of simplify it if you move logic from before insert to after insert, you can then query everything from DB... But it's weak, it's a validation that should prevent save, it logically belongs in before. It'll waste account id, maybe some autonumbers... Not elegant.
On update you should handle update of Channel but also of Account Id (reparenting to another record!). Otherwise I'll create consent with acc1 and move it to acc2.
What about undelete scenario? I create 1 consent, delete it, create identical one and restore 1st one from Recycle Bin. If you didn't cover after undelete - boom, headshot.
Instead go with pure config route (or simple trigger), let the database handle that for you.
Make a helper text field, mark it unique.
Write a workflow / process builder / simple trigger (before insert, before update) that writes to this field combination of Account__c + ' ' + PE_Channel__c. Condition could be ISNEW() || ISCHANGED(Account__c) || ISCHANGED(PE_Channel__c)
Optionally prepare data fix to update existing records.
Job done, you can't break it now. And if you ever need to allow more combinations (3rd field) it's easy for admin to extend it. As long as you keep under 255 chars total.
Or (even better) there are duplicate matching rules ;) give them a go before you do anything custom? Maybe check https://trailhead.salesforce.com/en/content/learn/modules/sales_admin_duplicate_management out.
To give a simplified example:
I have a database with one table: names, which has 1 million records each containing a common boy or girl's name, and more added every day.
I have an application server that takes as input an http request from parents using my website 'Name Chooser' . With each request, I need to pick up a name from the db and return it, and then NOT give that name to another parent. The server is concurrent so can handle a high volume of requests, and yet have to respect "unique name per request" and still be high available.
What are the major components and strategies for an architecture of this use case?
From what I understand, you have two operations: Adding a name and Choosing a name.
I have couple of questions:
Qustion 1: Do parents choose names only or do they also add names?
Question 2 If they add names, doest that mean that when a name is added it should also be marked as already chosen?
Assuming that you don't want to make all name selection requests to wait for one another (by locking of queueing them):
One solution to resolve concurrency in case of choosing a name only is to use Optimistic offline lock.
The most common implementation to this is to add a version field to your table and increment this version when you mark a name as chosen. You will need DB support for this, but most databases offer a mechanism for this. MongoDB adds a version field to the documents by default. For a RDBMS (like SQL) you have to add this field yourself.
You havent specified what technology you are using, so I will give an example using pseudo code for an SQL DB. For MongoDB you can check how the DB makes these checks for you.
NameRecord {
id,
name,
parentID,
version,
isChosen,
function chooseForParent(parentID) {
if(this.isChosen){
throw Error/Exception;
}
this.parentID = parentID
this.isChosen = true;
this.version++;
}
}
NameRecordRepository {
function getByName(name) { ... }
function save(record) {
var oldVersion = record.version - 1;
var query = "UPDATE records SET .....
WHERE id = {record.id} AND version = {oldVersion}";
var rowsCount = db.execute(query);
if(rowsCount == 0) {
throw ConcurrencyViolation
}
}
}
// somewhere else in an object or module or whatever...
function chooseName(parentID, name) {
var record = NameRecordRepository.getByName(name);
record.chooseForParent(parentID);
NameRecordRepository.save(record);
}
Before whis object is saved to the DB a version comparison must be performed. SQL provides a way to execute a query based on some condition and return the row count of affected rows. In our case we check if the version in the Database is the same as the old one before update. If it's not, that means that someone else has updated the record.
In this simple case you can even remove the version field and use the isChosen flag in your SQL query like this:
var query = "UPDATE records SET .....
WHERE id = {record.id} AND isChosend = false";
When adding a new name to the database you will need a Unique constrant that will solve concurrenty issues.
I'm in OPA for some days now and I really start to like it. I'm attending the first year of computer science and we make some database class the next year-
The little I know about Databases are from php, I have used MySQL with php and SQLlite with c++. But this type of database is a bit different from what I've seen.
I have followed the guide about database in OPA http://doc.opalang.org/manual/Hello--database but I have a question:
In the guide we declare a new Database:
type user_status = {regular} or {premium} or {admin}
type user_id = int
type user = { user_id id, string name, int age, user_status status }
database users {
user /all[{id}]
/all[_]/status = { regular }
}
We learn how to read this database and make some query to this database with Maps, but how do I add a new element? I was testing a bit:
/users/all[{id:0}]/name<-getusername;
but id should be auto increment, from the little I know.
Thanks everyone for the help =D
I really want to get in OPA, the little I have make is really impressive!
mongoDB and auto-increment
With mongoDB (the default Opa database) there is no auto-increment (like in SQL), for scalability reason.
But if you really need one, you can use a counter to create this feature yourself:
database users {
user /all[{id}]
int /fresh_key
/all[_]/status = { regular }
}
And increment the key each time you use it: /users/fresh_key++
Random fresh key
You can also generate a random id, for example with something like Random.string(6)
Read this thread to learn more about this technique: http://lists.owasp.org/pipermail/opa/2012-April/001052.html
User defined unique key
But if you are dealing with users, maybe you already have a unique key: what about using "login" or "email" as the unique key?
You can also use Date.in_milliseconds(Date.now_gmt()) for a more unique id, maybe concatenated with the user id
I have some data recieved from a simple HTML form like this:
$newdata =
array('Testing'=>array(
'topic'=>$data['Testing']['topic'],
'content'=>$data['Testing']['content']),
'new'=>$data['Testing']['new'])
);
The data has been added into the database using this line of code:
$this->Testing->save($newdata);
The data has been added into the database successfully,
but I am not sure if it is possible to retrieve the ID of this new record of data immediately after adding it into the database?
$this->Testing->id will contain the ID of the newly inserted record, but if you only need to know if the data was saved, you can check the return value of save(), which is false on failure.