I am trying to delete multiple keys in from couchbase in one call. Do we have something like bulkGet for delete in couchbase?
Bulk delete is definitely there, but it requires you to pass KEYs to be deleted as argument list. So it might not be possible to delete all the required records in just one call. Essentially, what you would be doing is (refer this link for an example):
Query the data from the Couchbase
Iterate over resultset
and fire delete for each key of your interest.
However, I believe: Delete on server should be delete on server, rather than requiring three steps as above.
In this regards, I think old fashioned RDBMS were better all you need to do is fire SQL query like 'DELETE * from database where something like "match%"'.
Fortunately, there is something similar to SQL is available in CouchBase called N1QL (pronounced nickle). I am not aware about JavaScript (and other language syntax) but this is how I did it in python.
Query to be used: DELETE from b where META(b).id LIKE "%"
layer_name_prefix = cb_layer_key + "|" + "%"
query = ""
try:
query = N1QLQuery('DELETE from `test-feature` b where META(b).id LIKE $1', layer_name_prefix)
cb.n1ql_query(query).execute()
except CouchbaseError, e:
logger.exception(e)
To achieve the same thing: alternate query could be as below if you are storing 'type' and/or other meta data like 'parent_id'.
DELETE from where type='Feature' and parent_id=8;
But I prefer to use first version of the query as it operates on key, and I believe Couchbase must have some internal indexes to operate/query faster on key (and other metadata).
Related
Consider this code. This code inserts the row to the database if it is not found, then only updates it if the row is found. The updateNode() method gives the entity some values based on the user input, so I called it in both cases.
session.beginTransaction();
node = (Node)session.createQuery("from Node").uniqueResult();
if (node == null) {
node = new Node();
updateNode();
session.save(node);
} else {
updateNode();
}
session.getTransaction.commit();
Is there a better way of checking if rows exist in the table aside from using queries?
Is the cat alive or dead? You don't know without checking it, so you'll have to execute the query in the database.
I assume your question is about to avoid writing such a query manually, but rather letting Hibernate do it itself. Then you may want to look at querying by example/prototype.
Regardless of the approach taken, keep concurrency issues in mind though; you may want to apply some unique constraints and/or optimistic/pessimistic locks.
The only way to find out if something already exists in the database is to query it. However you do not need a separate query. You need only one query and not two thanks to mysql's INSERT... ON DUPLICATE KEY UPDATE feature. And it doesn't need any additional java coding either.
If you want to do this with hibernate it will have to be a custom query and you will need to return the inserted row id with LAST_INSERT_ID in your query.
Have you heard of SQL Closures or any library that implements them ?
They allow to execute this script in SQL command window (or put it into SP):
exec closure,"
rec{select db=name from sys.databases where name like 'corp_'},{
use |db|
rec{select tbl=name from sys.tables where name like 'user_'},{
for{col},{Created,Modified},{
def_col {
|tbl|.|col| datetime not null default(getdate()) ix
}
}
def_col {|tbl|.deleted datetime ix}
}
}
"
This script will make sure that Created not null, Modified not null and Deleted indexed columns exist in all tables with prefix user_ in all databases with prefix corp_.
def_col will create new column or alter existing column to match desired definition. It will also create/recreate non-unique ascending index for each of these columns.
def_col will drop and recreate dependencies as needed (constraints, indexes, foreign keys, schema bound views and functions).
rec and for and def_col will catch errors and log them into error table or raise immediately depending on context options for easy debugging and tracking of errors during script execution should they happen.
As you can see, the script can be executed many times without failures, it's just second time it will not change anything.
Is there a more readable, supportable and compact way to achieve the same functionality in MS-SQL ?
If yes - please post example in your answer.
Is more readable, supportable and compact way available in MySql, Oracle or other major flavors of SQL language ?
I do not see any reason you could not create simple SQL Server Groups in SSMS, and register your servers against those groups and run your DDL from there. You could also do it with SQLCMD, or Powershell.
Can I use REPLACE without patching ActiveRecord or executing raw SQL in Rails 4?
I just want to save a record only if there is no corresponding data in its table.
I know find_or_create_by method but I guess this generates twofold queries, SELECT and INSERT.
If there is another INSERT query between the two, it will fail, right?
Or am I worrying too much? (The system I'm working on is not a mission critical one.)
REPLACE is a MySQL extension to the SQL standard.
As ActiveRecord tries to be database agnostic as much as possible, I don't think adding behaviour of a specific database is a priority... last mention I found of people asking for it was on 2009 Forums.
Anyway, I'm not sure if using REPLACE would be the same as using find_or_create_by.
From MySQL Reference:
REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is inserted.
find_or_create_by behaves differently, since it will leave the record as it is, if it already exists:
# File 'activerecord/lib/active_record/relation.rb', line 200
def find_or_create_by(attributes, &block)
find_by(attributes) || create(attributes, &block)
end
Also, as you mentioned, find_or_create_by can have a race condition if you don't use it properly. You should use it like this (from ActiveRecord Documentation):
begin
CreditAccount.find_or_create_by(user_id: user.id)
rescue ActiveRecord::RecordNotUnique
retry
end
Here is a chunk of the SQL I'm using for a Perl-based web application. I have a number of requests and each has a number of accessions, and each has a status. This chunk of code is there to update the table for every accession_analysis that shares all these fields for each accession in a request.
UPDATE accession_analysis
SET analysis_id = ? ,
reference_id = ? ,
status = ? ,
extra_parameters = ?
WHERE analysis_id = ?
AND reference_id = ?
AND status = ?
AND extra_parameters = ?
and accession_id is (
SELECT accesion_id
FROM accessions
where request_id = ?
)
I have changed the tables so that there's a status table for accession_analysis, so when I update, I update both accession_analysis and accession_analysis_status, which has status, status_text and the id of the accession_analysis, which is a not null auto_increment variable.
I have no strong idea about how to modify this code to allow this. My first pass grabbed all the accessions and looped through them, then filtered for all the fields, then updated. I didn't like that because I had many connections with short SQL commands, which I understood to be bad, but I can't help but think the only way to really do this is to go back to the loop in Perl holding two simpler SQL statements.
Is there a way to do this in SQL that, with my relative SQL inexperience, I'm just not seeing?
The answer depends on which DBMS you're using. The easiest way is to create a trigger on one table that provides the logic of updating the other table. (For any DB newbies -- a trigger is procedural code attached to a table at the DBMS (not application) layer that runs in response to an insert, update or delete on the table.). A similar, slightly less desirable method is to put the logic in a stored procedure and execute that instead of the update statement you're now using.
If the DBMS you're using doesn't support either of these mechanisms, then there isn't a good way to do what you're after while guaranteeing transactional integrity. However if the problem you're solving can tolerate a timing difference in the two tables' updates (i.e. The data in one of the tables is only used at predetermined times, like reporting or some type of batched operation) you could write to one table (live) and create a separate process that runs when needed (later) to update the second table using data from the first table. The correctness of allowing data to be updated at different times becomes a large and immovable design assumption, however.
If this is mostly about connection speed, then one option you have is to write a stored procedure that handles the "double update or insert" transparently. See the manual for stored procedures:
http://dev.mysql.com/doc/refman/5.5/en/create-procedure.html
Otherwise, You probably cannot do it in one statement, see the MySQL INSERT syntax:
http://dev.mysql.com/doc/refman/5.5/en/insert.html
The UPDATE syntax allows for multi-table updates (not in combination with INSERT, though):
http://dev.mysql.com/doc/refman/5.5/en/update.html
Each table needs its own INSERT / UPDATE in the query.
In fact, even if you create a view by JOINing multiple tables, when you INSERT into the view, you can only INSERT with fields belonging to one of the tables at a time.
The modifications made by the INSERT statement cannot affect more than one of the base tables referenced in the FROM clause of the view. For example, an INSERT into a multitable view must use a column_list that references only columns from one base table. For more information about updatable views, see CREATE VIEW.
Inserting data into multiple tables through an sql view (MySQL)
INSERT (SQL Server)
Same is true of UPDATE
The modifications made by the UPDATE statement cannot affect more than one of the base tables referenced in the FROM clause of the view. For more information on updatable views, see CREATE VIEW.
However, you can have multiple INSERTs or UPDATEs per query or stored procedure.
I need the sample program in Java for keeping the history of table if user inserted, updated and deleted on that table. Can anybody help in this?
Thanks in advance.
If you are working with Hibernate you can use Envers to solve this problem.
You have two options for this:
Let the database handle this automatically using triggers. I don't know what database you're using but all of them support triggers that you can use for this.
Write code in your program that does something similar when inserting, updating and deleting a user.
Personally, I prefer the first option. It probably requires less maintenance. There may be multiple places where you update a user, all those places need the code to update the other table. Besides, in the database you have more options for specifying required values and integrity constraints.
Well, we normally have our own history tables which (mostly) look like the original table. Since most of our tables already have the creation date, modification date and the respective users, all we need to do is copy the dataset from the live table to the history table with a creation date of now().
We're using Hibernate so this could be done in an interceptor, but there may be other options as well, e.g. some database trigger executing a script, etc.
How is this a Java question?
This should be moved in Database section.
You need to create a history table. Then create database triggers on the original table for "create or replace trigger before insert or update or delete on table for each row ...."
I think this can be achieved by creating a trigger in the sql-server.
you can create the TRIGGER as follows:
Syntax:
CREATE TRIGGER trigger_name
{BEFORE | AFTER } {INSERT | UPDATE |
DELETE } ON table_name FOR EACH ROW
triggered_statement
you'll have to create 2 triggers one for before the operation is performed and another after the operation is performed.
otherwise it can be achieved through code also but it would be a bit tedious for the code to handle in case of batch processes.
You should try using triggers. You can have a separate table (exact replica of your table of which you need to maintain history) .
This table will then be updated by trigger after every insert/update/delete on your main table.
Then you can write your java code to get these changes from the second history table.
I think you can use the redo log of your underlying database to keep track of the operation performed. Is there any particular reason to go for the program?
You could try creating say a List of the objects from the table (Assuming you have objects for the data). Which will allow you to loop through the list and compare to the current data in the table? You will then be able to see if any changes occurred.
You can even create another list with a object that contains an enumerator that gives you the action (DELETE, UPDATE, CREATE) along with the new data.
Haven't done this before, just a idea.
Like #Ashish mentioned, triggers can be used to insert into a seperate table - this is commonly referred as Audit-Trail table or audit log table.
Below are columns generally defined in such audit trail table : 'Action' (insert,update,delete) , tablename (table into which it was inserted/deleted/updated), key (primary key of that table on need basis) , timestamp (the time at which this action was done)
It is better to audit-log after the entire transaction is through. If not, in case of exception being passed back to code-side, seperate call to update audit tables will be needed. Hope this helps.
If you are talking about db tables you may use either triggers in db or add some extra code within your application - probably using aspects. If you are using JPA you may use entity listeners or perform some extra logic adding some aspect to your DAO object and apply specific aspect to all DAOs which perform CRUD on entities that needs to sustain historical data. If your DAO object is stateless bean you may use Interceptor to achive that in other case use java proxy functionality, cglib or other lib that may provide aspect functionality for you. If you are using Spring instead of EJB you may advise your DAOs within application context config file.
Triggers are not suggestable, when I stored my audit data in file else I didn't use the database...my suggestion is create table "AUDIT" and write java code with help of servlets and store the data in file or DB or another DB also ...