How do I use wild character in MongoDB while use Update
I want to do like below in mongo db is it possible to write it.
update emp set sal=sal*2 where ename like '%Pr%';
emp is the collection name
columns: ename, eno, sal
You can use a regexp for your wildcard search, but you have to do the update client-side, because mongoDB is not able to access the content of another field (or the field's content itself) while updating:
db.emp.find( { ename: /Pr/ } ).forEach( function (x) {
x.sal = x.sal * 2;
db.emp.save( x );
});
In MongoDB 2.6 you will be able to do that update enirely server-side using the new $mul operator. As of the time of this posting 2.6 is still in pre-relase; you can check the MongoDB download page for availability. Check the release notes for a complete list of changes and new features.
Also note that you should use an anchored regexp query, that is one that begins with ^, if you know that the string you are searching for is at the beginning of the field. Anchored regexp queries are more efficient because they can use an index and avoid a table scan.
Here is the query with these two changes:
db.emp.update({ename: /^Pr/}, {$mul: {sal: 2}}, {multi: true})
Related
When I create an Index on a string-type field in MongoDB I get no significant speed boost from it. In fact, when I use the query:
db.movies.find({plot: /some text/}).explain("executionStats")
An Index is slowing down the query by 30-50% in my Database (~55k Docs).
I know, that I can use a "text" Index, which is working fine for me, but I was wondering, why you would create a "normal" Index on a string field.
Index on string fields will improve the performance of exact matches like,
db.movies.find({name: "some movie"})
Indexes will also be used for find queries with prefix expression,
db.movies.find({plot: /^begins with/})
I need to find all the documents in mongodb that have keywords that start with number 1-9, then add a '+' in front of the keyword, I can easily find the documents but cannot figure out how to update them.
I tried this one, but it doesn't work
db.placements.update({program_id:{$in:[113,107]},
keyword:{$regex:'^[0-9]', $options:'i'}},
{keyword:"+"+$keyword})
It cannot recognize $keyword, I also tried '.keyword', 'keyword', none of them works. Is there any way to reference the document itself like Java does, using 'this', so I can do something like
this.keyword: "+" + this.keyword
You'll have to use the $set operator in the update query to update a specific field. Also, you cannot concatenate string within an update query. One way to do this would be using cursor forEach() in the shell:
db.placements.find({program_id:{$in:[113,107]}, keyword:{$regex:'^[0-9]', $options:'i'}})
.forEach(function(doc){
db.placements.updateOne({_id:doc._id}, {$set:{"keyword":"+" + doc.keyword}})
})
No, you cannot reference a value on the document itself when querying like you can with SQL.
I would suggest querying the document, updating it on your web/app server and then updating the value back to mongodb.
You will also find that your update command above will wipe your entire document leaving only the keyword field. You should use the $set modifier to update a field or set of fields.
db.placements.update(
{
program_id:{$in:[113,107]},
keyword:{$regex:'^[0-9]', $options:'i'}
},
{ $set: {keyword: new_value}})
How do you do nested select in MongoDB analogous to
SELECT id FROM table1 WHERE id IN (SELECT id FROM table2)
MongoDB does not yet possess the ability to do subqueries which would allow this functionality.
I am sure it is something within the JIRA however, I could not immediately find it.
The only way currently is to actually pick the table, iterate the cursor pulling out the information and using that as part of a $in query as shown by #Bruno, like so:
ids=[];
for(i in db.c2.find({},{_id:1}){ // I have assumed id=_id
ids[ids.length]=i; // The default return of the index pos is actually _id
}
return db.c1.find({$in:ids});
As a mere example I wrote off of the top of my head.
This page contains comparator between SQL and MongoDB:
http://docs.mongodb.org/manual/reference/sql-comparison/
For example, you can to use a aggregation pipeline and where is the same as:
db.your_collection.aggregate({$match: {"id": {$in: ['id_0', 'id_1']} }})
A simple query as the same as:
db.your_collection.aggregate({field: "value"})
Mongodb official page has a lot of informations
I am trying to use upsert in MongoDB to update a single field in a document if found OR insert a whole new document with lots of fields. The problem is that it appears to me that MongoDB either replaces every field or inserts a subset of fields in its upsert operation, i.e. it can not insert more fields than it actually wants to update.
What I want to do is the following:
I query for a single unique value
If a document already exists, only a timestamp value (lets call it 'lastseen') is updated to a new value
If a document does not exists, I will add it with a long list of different key/value pairs that should remain static for the remainder of its lifespan.
Lets illustrate:
This example would from my understanding update the 'lastseen' date if 'name' is found, but if 'name' is not found it would only insert 'name' + 'lastseen'.
db.somecollection.update({name: "some name"},{ $set: {"lastseen": "2012-12-28"}}, {upsert:true})
If I added more fields (key/value pairs) to the second argument and drop the $set, then every field would be replaced on update, but would have the desired effect on insert. Is there anything like $insert or similar to perform operations only when inserting?
So it seems to me that I can only get one of the following:
The correct update behavior, but would insert a document with only a subset of the desired fields if document does not exist
The correct insert behavior, but would then overwrite all existing fields if document already exists
Are my understanding correct? If so, is this possible to solve with a single operation?
MongoDB 2.4 has $setOnInsert
db.somecollection.update(
{name: "some name"},
{
$set: {
"lastseen": "2012-12-28"
},
$setOnInsert: {
"firstseen": <TIMESTAMP> # set on insert, not on update
}
},
{upsert:true}
)
There is a feature request for this ( https://jira.mongodb.org/browse/SERVER-340 ) which is resolved in 2.3. Odd releases are actually dev releases so this will be in the 2.4 stable.
So there is no real way in the current stable versions to do this yet. I am afraid the only method is to actually do 3 conditional queries atm: 1 to check the row, then a if to either insert or update.
I suppose if you had real problems with lock here you could do this function with sole JS but that's evil however it would lock this update to a single thread.
I am trying to use upsert in MongoDB to update a single field in a document if found OR insert a whole new document with lots of fields. The problem is that it appears to me that MongoDB either replaces every field or inserts a subset of fields in its upsert operation, i.e. it can not insert more fields than it actually wants to update.
What I want to do is the following:
I query for a single unique value
If a document already exists, only a timestamp value (lets call it 'lastseen') is updated to a new value
If a document does not exists, I will add it with a long list of different key/value pairs that should remain static for the remainder of its lifespan.
Lets illustrate:
This example would from my understanding update the 'lastseen' date if 'name' is found, but if 'name' is not found it would only insert 'name' + 'lastseen'.
db.somecollection.update({name: "some name"},{ $set: {"lastseen": "2012-12-28"}}, {upsert:true})
If I added more fields (key/value pairs) to the second argument and drop the $set, then every field would be replaced on update, but would have the desired effect on insert. Is there anything like $insert or similar to perform operations only when inserting?
So it seems to me that I can only get one of the following:
The correct update behavior, but would insert a document with only a subset of the desired fields if document does not exist
The correct insert behavior, but would then overwrite all existing fields if document already exists
Are my understanding correct? If so, is this possible to solve with a single operation?
MongoDB 2.4 has $setOnInsert
db.somecollection.update(
{name: "some name"},
{
$set: {
"lastseen": "2012-12-28"
},
$setOnInsert: {
"firstseen": <TIMESTAMP> # set on insert, not on update
}
},
{upsert:true}
)
There is a feature request for this ( https://jira.mongodb.org/browse/SERVER-340 ) which is resolved in 2.3. Odd releases are actually dev releases so this will be in the 2.4 stable.
So there is no real way in the current stable versions to do this yet. I am afraid the only method is to actually do 3 conditional queries atm: 1 to check the row, then a if to either insert or update.
I suppose if you had real problems with lock here you could do this function with sole JS but that's evil however it would lock this update to a single thread.