In cassandra 2.2, we can iterate update to get the cell change value:
for (Cell cell : update)
{
// Skip the row marker and other empty values, since they lead to an empty key.
if (cell.value().remaining() > 0)
{
Mutation mutation = new Mutation(indexKeySpace, cell.value());
mutation.add(indexColumnFamily, cell.name(), key, System.currentTimeMillis());
mutations.add(mutation);
}
}
In cassandra 3.0, the ITrigger interface was changed, and the current object is change to "Partition update":
public Collection<Mutation> augment(Partition update)
If anyone know what's the proper way to extract the detail change value of each cell?
Related
Hi I am newbie to dynamoDB. Below is the schema of the dynamo table
{
"user_id":1, // partition key
"dob":"1991-09-12", // sort key
"movies_watched":{
"1":{
"movie_name":"twilight",
"movie_released_year":"1990",
"movie_genre":"action"
},
"2":{
"movie_name":"harry potter",
"movie_released_year":"1996",
"movie_genre":"action"
},
"3":{
"movie_name":"lalaland",
"movie_released_year":"1998",
"movie_genre":"action"
},
"4":{
"movie_name":"serendipity",
"movie_released_year":"1999",
"movie_genre":"action"
}
}
..... 6 more attributes
}
I want to insert a new item if the item(that user id with dob) did not exist, otherwise add the movies to existing movies_watched map by checking if the movie is not already available the movies_watched map .
Currently, I am trying to use update(params) method.
Below is my approach:
function getInsertQuery (item) {
const exp = {
UpdateExpression: 'set',
ExpressionAttributeNames: {},
ExpressionAttributeValues: {}
}
Object.entries(item).forEach(([key, item]) => {
if (key !== 'user_id' && key !== 'dob' && key !== 'movies_watched') {
exp.UpdateExpression += ` #${key} = :${key},`
exp.ExpressionAttributeNames[`#${key}`] = key
exp.ExpressionAttributeValues[`:${key}`] = item
}
})
let i = 0
Object.entries(item. movies_watched).forEach(([key, item]) => {
exp.UpdateExpression += ` movies_watched.#uniqueID${i} = :uniqueID${i},`
exp.ExpressionAttributeNames[`#uniqueID${i}`] = key
exp.ExpressionAttributeValues[`:uniqueID${i}`] = item
i++
})
exp.UpdateExpression = exp.UpdateExpression.slice(0, -1)
return exp
}
The above method just creates update expression with expression names and values for all top level attributes as well as nested attributes (with document path).
It works well if the item is already available by updating movies_watched map. But throws exception if the item is not available and while inserting. Below is exception:
The document path provided in the update expression is invalid for update
However, I am still not sure how to check for duplicate movies in movies_watched map
Could someone guide me in right direction, any help is highly appreciated!
Thanks in advance
There is no way to do this, given your model, without reading an item from DDB before an update (at that point the process is trivial). If you don't want to impose this additional read capacity on your table for update, then you would need to re-design your data model:
You can change movies_watched to be a Set and hold references to movies. Caveat is that Set can contain only Numbers or Strings, thus you would have movie id or name or keep the data but as JSON Strings in your Set and then parse it back into JSON on read. With SET you can perform ADD operation on the movies_watched attribute. https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.ADD
You can go with single table design approach and have these movies watched as separate items with (PK:userId and SK:movie_id). To get a user you would perform a query and specify only PK=userId -> you will get a collection where one item is your user record and others are movies_watched. If you are new to DynamoDB and are learning the ropes, then I would suggest go with this approach. https://www.alexdebrie.com/posts/dynamodb-single-table/
I am trying to create a trigger in APEX, when an custom textfield of an custom sObject gets updated with products (means, when new products get insert or existing one get deleted).
How can I compare in APEX the Trigger.Old values with the Trigger? New values of this field in order to start the Trigger.
It would look something like this:
Trigger NameOfTrigger on CustomSObject__c (after update){
/*there is already an existing list of products that get insert into the custom textfield (probably as Strings)
*/
List <String> textList = new List <String> ();
/*PseudoCode: if the textfield got updated/has changed, copy from every entry of this textfield (entry = product name as a string) and copy fieldX into another sObject
*/
if(CustomSObject.field(OldValues) != CustomSObject.field(NewValues)){
for (String product : textList){
//Trigger e.g. copy the values of a certain field of p and paste them in another sObject
}
Could somebody help me with the syntax?
You can utilize inbuilt Trigger.new and Trigger.old to get the latest and old values of any record. These lists can be used to achieve what you're looking for.
Sample example would be:
Trigger NameOfTrigger on CustomSObject__c (after update){
for(CustomSObject__c customObject : Trigger.new) {
// get old record
CustomSObject__c oldCustomObject = Trigger.oldMap.get(customObject.Id);
// compare old and new values of a particular field
if(customObject.fieldName != oldCustomObject.fieldName){
//Trigger e.g. copy the values of a certain field of p and paste them in another sObject
}
}
}
See documentation of Trigger.new & Trigger.old
How insert item on top table in PostgreSQL? That it is possible? In the table I have only two fields as text. First is primary key.
CREATE TABLE news_table (
title text not null primary key,
url text not null
);
I need a simple query for the program in java.
OK, this is my code:
get("/getnews", (request, response) -> {
List<News> getNews = newsService.getNews();
List<News> getAllNews = newsService.getAllNews();
try (Connection connection = DB.sql2o.open()) {
String sql = "INSERT INTO news_table(title, url) VALUES (:title, :url)";
for (News news : getNews) {
if (!getAllNews.contains(news)) {
connection.createQuery(sql, true)
.addParameter("title", news.getTitle())
.addParameter("url", news.getUrl())
.executeUpdate()
.getKey();
}
}
}
return newsService.getNews();
}, json());
The problem is that as it calls getnews method for the second time this new news adds at the end of the table, and there is no extant hronologi news. How this resolve? I use Sql2o + sparkjava.
Probably already I know. I need to reverse the List getnews before I will must contains object getnews and getallnews?
There is no start or end in a table. If you want to sort your data, just use an ORDER BY in your SELECT statements. Without ORDER BY, there is no order.
Relational theory, the mathematical foundation of relational databases, lays down certain conditions that relations (represented in real databases as tables) must obey. One of them is that they have no ordering (i.e., the rows will neither be stored nor retrieved in any particular order, since they are treated as a mathematical set). It's therefore completely under the control of the RDBMS where a new row is entered into a table.
Hence there is no way to ensure a particular ordering of the data without using an ORDER BY clause when you retrieve the data.
I am using EntityFramework in my Apllication. If I want to fetch one table value means that will return values with all the referenced table values. It takes time to fetch all the table values. If I need one specified reference table values means
How do I Prevent fetching other reference table values?
If you want to extract single table record without reference tables so you need to define LazyLoadingEnabled false in your DBContext class.
Example your database name is EmpReview
public class UserDataLayerContext : DbContext
{
public UserDataLayerContext()
: base("name=EmpReview")
{
this.Configuration.LazyLoadingEnabled = false;
}
So all the DBSet classes which in UserDataLayerContext filter time only get the single table record without any reference class.
Using this.Configuration.LazyLoadingEnabled = false; none of return reference table calss but in that you need to get single reference table check below example,
Suppose one table class is UserMaster and it is link to GroupMaster master
So
return context.UserMasters.Include("GroupMaster").Where(x => (x.UserID == id) && (x.IsActive ==
true)).ToList();
In that case you get all the usermaster record with group master table.
And
return context.UserMasters.Where(x => (x.UserID == id) && (x.IsActive == true)).ToList();
above case you get all the record of usermaster with out group master table.
I'm new to Couchbase and am struggling to get a composite index to do what I want it to. The use-case is this:
I have a set of "Enumerations" being stored as documents
Each has a "last_updated" field which -- as you may have guessed -- stores the last time that the field was updated
I want to be able to show only those enumerations which have been updated since some given date but still sort the list by the name of the enumeration
I've created a Couchbase View like this:
function (doc, meta) {
var time_array;
if (doc.doc_type === "enum") {
if (doc.last_updated) {
time_array = doc.last_updated.split(/[- :]/);
} else {
time_array = [0,0,0,0,0,0];
}
for(var i=0; i<time_array.length; i++) { time_array[i] = parseInt(time_array[i], 10); }
time_array.unshift(meta.id);
emit(time_array, null);
}
}
I have one record that doesn't have the last_updated field set and therefore has it's time fields are all set to zero. I thought as a first test I could filter out that result and I put in the following:
startkey = ["a",2012,0,0,0,0,0]
endkey = ["Z",2014,0,0,0,0,0]
While the list is sorted by the 'id' it isn't filtering anything! Can anyone tell me what I'm doing wrong? Is there a better composite view to achieve these results?
In couchbase when you query view by startkey - endkey you're unable to filter results by 2 or more properties. Couchbase has only one index, so it will filter your results only by first param. So your query will be identical to query with:
startkey = ["a"]
endkey = ["Z"]
Here is a link to complete answer by Filipe Manana why it can't be filtered by those dates.
Here is a quote from it:
For composite keys (arrays), elements are compared from left to right and comparison finishes as soon as a element is different from the corresponding element in the other key (same as what happens when comparing strings à la memcmp() or strcmp()).
So if you want to have a view that filters by date, date array should go first in composite key.