Using the example from the article Using lightweight transactions, the example of such a transaction is given as:
UPDATE cycling.cyclist_name
SET firstname = 'Roxane'
WHERE id = 4647f6d3-7bd2-4085-8d6c-1229351b5498
IF firstname = 'Roxxane';
How is this different from replacing IF with WHERE, as in:
UPDATE cycling.cyclist_name
SET firstname = 'Roxane'
WHERE id = 4647f6d3-7bd2-4085-8d6c-1229351b5498
AND firstname = 'Roxxane';
I am guessing that the second one does not do the read and write in a single step, but rather first selects based on where and then applies the update, while the first one blocks other processes from writing to the DB when the query is running.
In case of concurrent update from two different client, The first query will assure that only one is applied at a time (assuming NOT using NON-SERIAL consistency) however that is not true for 2nd update. Check this.
Related
like the title mentions I want a Query that gets a random row of the existing database. After that I want to save the data which is in a specific column of that row in a variable for further purposes.
The query I have at the moment is as follows:
#Query("SELECT * FROM data_table ORDER BY RANDOM() LIMIT 1")
fun getRandomRow()
For now I am not sure if this query even works, but how would I go about writing my function to pass a specific column of that randomly selected row to a variable?
Ty for your advice, tips and/or solutions!
Your query is almost correct; however, you should specify a return type in the function signature. For example, if the records in the data_table table are mapped using a data class called DataEntry, then the query could read as shown below (note I've also added the suspend modifier so the query must be run using a coroutine):
#Query("SELECT * FROM data_table ORDER BY RANDOM() LIMIT 1")
suspend fun getRandomRow(): DataEntry?
If your application interacts with the database via a repository and view model (as described here: https://developer.android.com/topic/libraries/architecture/livedata) then the relevant methods would be along the lines of:
DataRepository
suspend fun findRandomEntry(): DataEntry? = dataEntryDao.getRandomRow()
DataViewModel
fun getRandomRecord() = viewModelScope.launch(Dispatchers.IO) {
val entry: DataEntry? = dataRepository.findRandomEntry()
entry?.let {
// You could assign a field of the DataEntry record to a variable here
// e.g. val name = entry.name
}
}
The above code uses the view model's coroutine scope to query the database via the repository and retrieve a random DataEntry record. Providing the returning DataEntry record is not null (i.e. your database contains data) then you could assign the fields of the DataEntry object to variables in the let block of the getRandomRecord() method.
As a final point, if it's only one field that you need, you could specify this in the database query. For example, imagine the DataEntry data class has a String field called name. You could retrieve this bit of information only and ignore the other fields by restructuring your query as follows:
#Query("SELECT name FROM data_table ORDER BY RANDOM() LIMIT 1")
suspend fun getRandomRow(): String?
If you go for the above option, remember to refactor your repository and view model to expect a String instead of a DataEntry object.
I have a table whose column types are
text, bigint, set<text>
I'm trying to update a single row and add an element to the set using QueryBuilder.
The code that overwrites the existing set looks like this (note this is scala):
val query = QueryBuilder.update("twitter", "tweets")
.`with`(QueryBuilder.set("sinceid", update.sinceID))
.and(QueryBuilder.set("tweets", setAsJavaSet(update.tweets)))
.where(QueryBuilder.eq("handle", update.handle))
I was able to find the actual CQL for adding an element to a set which is:
UPDATE users
SET emails = emails + {'fb#friendsofmordor.org'} WHERE user_id = 'frodo';
But could not find an example using QueryBuilder.
Based off of the CQL I also tried:
.and(QueryBuilder.set("tweets", "tweets"+{setAsJavaSet(update.tweets)}))
But it did not work. Thanks in advance
Use add (add one element at a time) or addAll (more than one any number of element at a time) method to add to a set.
To extend Ananth's answer:
QueryBuilder.add does not support BindMarker. To use BindMarker while adding in set, it is required to use QueryBuilder.addAll only.*
*Just a note, Collections.singleton may come in handy in this regard.
Using #Ananth and #sazzad answers, the code below works:
Session cassandraSession;
UUID uuid;
Long value;
Statement queryAddToSet = QueryBuilder
.update("tableName")
.with(QueryBuilder.addAll("setFieldName", QueryBuilder.bindMarker()))
.where(QueryBuilder.eq("whereFieldName", QueryBuilder.bindMarker()));
PreparedStatement preparedQuery = cassandraSession.prepare(queryAddToSet);
BoundStatement boundQuery = preparedQuery.bind();
boundQuery
.setUUID("whereFieldName", uuid)
.setSet("setFieldName", Collections.singleton(value));
session.execute(boundQuery);
I have a Paginated List displayed on the visual force page and in the backend I was using a StandardSetController to control the pagination. However, one column on the table is an aggregated field whose calculation is done in a wrapper class. Recently, I want to sort the paginated list against the calculated field. And unfortunately the calculated result cannot be done on the data model(SObject) level.
So I am thinking to passed a sorted list of SObject to the StandardSetController constructor. That is to sort the record before it has been pass into the StandardSetController.
The code is like below:
List<Job__c> jobs = new List<Job__c>();
List<Job__c> tempJobs = Database.Query(basicQuery + filterExpression);
//sort with values
List<JobWrapper> jws = createJobWrappers(tempJobs);
JobWrapper.sortBy = JobWrapper.SORTBY_CALCULATEDFIELD_ASC;
jws.sort();
for(JobWrapper jw : jws){
jobs.add(jw.JobRecord);
}
jobs = jobs.deepClone(true, true, true);
StandardSetController con = new ApexPages.StandardSetController(jobs);
con.setPageSize(10);
However after executing the last line system throw exception:Modified rows exist in the records collection!
I did not modify any rows in the controller. Could anyone help me understanding the exception?
Objective:
I have a table called Publication that contains Id, RecordId, EntityType and a couple other columns. I select all the records that need to be published to another database from that table. I then loop that collection to process the records and move the records to the other db.
Background:
The EntityType column is used to Identify the Set that the context needs to retrieve. I also use reflection to create a object of that type to see if it implements a certain type of interface. If the record being processed does implement that interface then I know that the RecordId for that record in the Publication table is not a PK in the Set() but rather a FK.
this code works fine when I am going after the PK values for EntityTypes that do not inherit the specific interface.
object authoringRecordVersion = PublishingFactory.AuthoringContext.Set(recordType.Entity.GetType()).Find(record.RecordId);
Problem:
DbContext.Set(EntityType).Find(PK) goes after the PrimaryKey value. How can I tell Set() to search like this sudo code example since 'Where' is not allowed
object authoringRecordVersion = PublishingFactory.AuthoringContext.Set(recordType.Entity.GetType()).Where(c => c.HeaderRecordId == record.RecordId)
Update:
I am working on Implementing the following. Will advise results tomorrow
var sql = "SELECT * from " + record.Entity + " WHERE HeaderRecordId = '" + record.RecordId + "'";
authoringRecordVersion = PublishingFactory.AuthoringContext.Set(recordType.Entity.GetType()).SqlQuery(sql).AsNoTracking();
.SqlQuery(sql).AsNoTracking();
does work effectively. Don't know why I didn't see this earlier.
I have a search log with fields namely time, place and the query. I want to find the most queried word from a particular place between a particular time. All the fields namely date,time, query_String are chararrays. I have the below pig script but it doesnot do what is required.
Data = LOAD 'data' USING CustomPigStorage();
FClients = FILTER Data BY NOT(country is null);
Clients = FOREACH FClients GENERATE date,time, country,query_string as query;
grp = group Clients by (query, country, date, time);
wth_count = foreach grp generate FLATTEN(group), COUNT(Clients) as count;
For example, I want the result to be "between 2pm and 3 pm, hello was searched 4 times from USA".
I am basically confused by the Count() function .Relatively new to pig. I believe my count() here is counting the total number of records I have.
Your query looks correct, COUNT(Clients) returns number of records in the bag, that came from Clients and belong to the group. To see it you can remove COUNT from "wth_count" statement and save results into a file and than look into it.
wth_count = foreach grp generate group, Clients;
store wth_count into 'path';
Your potential problem might be in the fact that you are using date and time columns in the group by and they produce too many groups. To mitigate this you could write a java static function that gets date and time and returns a single value for the range, for example 12-07-2012, 14.05.03 is converted into "12-07-2012 14h" and 12-07-2012, 14.05.05 into "12-07-2012 14h". This will create a key that covers the time interval 2pm and 3pm and will put all of the records from Clinets into that group's bag.