[Couchdb Wiki] Update of "View_Snippets" by JoanTouzet

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- <>
  
- Please see our [[http://docs.couchdb.org/en/stable/ddocs/index.html|official 
documentation]] instead.
- 
- (All of the examples formerly on this page are better suited for the new 
[[http://docs.couchdb.org/en/stable/api/database/find.html|mango-based 
queries]], anyway.)
- 

[Couchdb Wiki] Update of "View_Snippets" by JoanTouzet

[Apache Wiki]

Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Couchdb Wiki" for 
change notification.

The "View_Snippets" page has been changed by JoanTouzet:
https://wiki.apache.org/couchdb/View_Snippets?action=diff=47=48

  
  Please see our [[http://docs.couchdb.org/en/stable/ddocs/index.html|official 
documentation]] instead.
  
- (All of the examples formerly on this page are better suited for the new 
[[http://docs.couchdb.org/en/2.1.1/api/database/find.html|mango-based 
queries]], anyway.)
+ (All of the examples formerly on this page are better suited for the new 
[[http://docs.couchdb.org/en/stable/api/database/find.html|mango-based 
queries]], anyway.)
  

[Couchdb Wiki] Update of "View_Snippets" by JoanTouzet

[Apache Wiki]

Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Couchdb Wiki" for 
change notification.

The "View_Snippets" page has been changed by JoanTouzet:
https://wiki.apache.org/couchdb/View_Snippets?action=diff=46=47

Comment:
Removing obsolete and not-recommended advice; point people to Mango instead

  <>
  
+ Please see our [[http://docs.couchdb.org/en/stable/ddocs/index.html|official 
documentation]] instead.
- = View Snippets =
- <>
  
- This page collects code snippets to be used in your [[Views]]. They are 
mainly meant to help get your head around the map/reduce approach to accessing 
database content.
+ (All of the examples formerly on this page are better suited for the new 
[[http://docs.couchdb.org/en/2.1.1/api/database/find.html|mango-based 
queries]], anyway.)
  
- '''Remember''': the Futon web client silently adds ''group=true'' to your 
views.
- 
- == Common mistakes ==
- When creating a reduce function, a re-reduce should behave in the same way as 
the regular reduce. The reason is that CouchDB doesn't necessarily call 
re-reduce on your map results.
- 
- Think about it this way: If you have a bunch of values ''V1 V2 V3'' for key 
''K'', then you can get the combined result either by calling 
''reduce([K,K,K],[V1,V2,V3],0)'' or by re-reducing the individual results: 
''reduce(null,[R1,R2,R3],1)''. This depends on what your view results look like 
internally.
- 
- == Get docs with a particular user id ==
- {{{#!highlight javascript
- // map
- function(doc) {
-   if (doc.user_id) {
- emit(doc.user_id, null);
-   }
- }
- }}}
- Then query with ''key=USER_ID'' to get all the rows that match that user.
- 
- == Get all documents which have an attachment ==
- This lists only the documents which have an attachment.
- 
- {{{#!highlight javascript
- // map
- function(doc) {
-   if (doc._attachments) {
- emit(doc._id, null);
-   }
- }
- }}}
- In SQL this would be something like {{{SELECT id FROM table WHERE attachment 
IS NOT NULL}}}.
- 
- == Count documents with and without an attachment ==
- Call this with ''group=true'' or you only get the combined number of 
documents with and without attachments.
- 
- {{{#!highlight javascript
- // map
- function(doc) {
-   if (doc._attachments) {
- emit("with attachment", 1);
-   }
-   else {
- emit("without attachment", 1);
-   }
- }
- }}}
- {{{#!highlight javascript
- // reduce
- function(keys, values) {
-return sum(values);
- }
- }}}
- Using curl you can call it like this:
- 
- {{{
- curl -s -i -X POST -H 'Content-Type: application/json'
-   -d '{"map": "function(doc){if(doc._attachments) {emit(\"with\",1);} else 
{emit(\"without\",1);}}",
-   "reduce": "function(keys, values) {return sum(values);}"}'
-   'http://localhost:5984/somedb/_temp_view?group=true'
- }}}
- In SQL this would be something along the lines of {{{SELECT num_attachments 
FROM table GROUP BY num_attachments}}} (but this would give extra output for 
rows containing more than one attachment).
- 
- == Generating a list of unique values ==
- Here we use the fact that the key for a view result can be an array. Suppose 
you have a map that generates (key, value) pairs with many duplicates and you 
want to remove the duplicates. To do so, use {{{emit([key, value], null)}}} as 
the map output.
- 
- Call this with ''group=true'' or you only get ''null''.
- 
- {{{#!highlight javascript
- // map
- function(doc) {
-   for (var i in doc.links)
- emit([doc.parent, i], null);
-   }
- }
- }}}
- {{{#!highlight javascript
- // reduce
- function(keys, values) {
-return null;
- }
- }}}
- This will give you results like
- 
- {{{#!highlight javascript
- {"rows":[
- {"key":["thisparent","thatlink"],"value":null},
- {"key":["thisparent","thatotherlink"],"value":null}
- ]}
- }}}
- You can then get all the rows for the key ''"thisparent"'' with the view 
parameters 
''startkey=["thisparent"]=["thisparent",{}]_end=false''
- 
- Note that the trick here is using the key for what you want to make unique. 
You can combine this with the counting above to get a count of duplicate values:
- 
- {{{#!highlight javascript
- // map
- function(doc) {
-   for (var i in doc.links)
- emit([doc.parent, i], 1);
-   }
- }
- }}}
- {{{#!highlight javascript
- // reduce
- function(keys, values) {
-return sum(values);
- }
- }}}
- If you then want to know the total count for each parent, you can use the 
''group_level'' view parameter: 
''startkey=["thisparent"]=["thisparent",{}]_end=false_level=1''
- 
- == Get contents of an object with specific attributes e.g. 
doc.objects.[0].attribute ==
- {{{#!highlight javascript
- // map
- function(doc) {
-   for (var idx in doc.objects) {
- emit(doc.objects[idx], attribute)
-   }
- }
- }}}
- == Arbitrarily query against any document property ("uniview") ==
- '''Note: This is not a generally recommended approach, as your view size will 
be (# of documents * # of document fields). '''However, if 

[Couchdb Wiki] Update of View_Snippets by JoanTouzet

[Apache Wiki]

Dear Wiki user,

You have subscribed to a wiki page or wiki category on Couchdb Wiki for 
change notification.

The View_Snippets page has been changed by JoanTouzet:
http://wiki.apache.org/couchdb/View_Snippets?action=diffrev1=45rev2=46

  = View Snippets =
  TableOfContents()
  
- This page collects code snippets to be used in your [[Views]]. They are 
mainly meant to help get your head around the map/reduce approach to accessing 
database content. 
+ This page collects code snippets to be used in your [[Views]]. They are 
mainly meant to help get your head around the map/reduce approach to accessing 
database content.
  
  '''Remember''': the Futon web client silently adds ''group=true'' to your 
views.
  
  == Common mistakes ==
- 
  When creating a reduce function, a re-reduce should behave in the same way as 
the regular reduce. The reason is that CouchDB doesn't necessarily call 
re-reduce on your map results.
  
  Think about it this way: If you have a bunch of values ''V1 V2 V3'' for key 
''K'', then you can get the combined result either by calling 
''reduce([K,K,K],[V1,V2,V3],0)'' or by re-reducing the individual results: 
''reduce(null,[R1,R2,R3],1)''. This depends on what your view results look like 
internally.
  
- 
  == Get docs with a particular user id ==
- 
  {{{#!highlight javascript
  // map
  function(doc) {
@@ -26, +23 @@

}
  }
  }}}
- 
  Then query with ''key=USER_ID'' to get all the rows that match that user.
  
- 
  == Get all documents which have an attachment ==
- 
  This lists only the documents which have an attachment.
  
  {{{#!highlight javascript
@@ -42, +36 @@

}
  }
  }}}
- 
  In SQL this would be something like {{{SELECT id FROM table WHERE attachment 
IS NOT NULL}}}.
  
- 
  == Count documents with and without an attachment ==
- 
  Call this with ''group=true'' or you only get the combined number of 
documents with and without attachments.
  
  {{{#!highlight javascript
@@ -57, +48 @@

  emit(with attachment, 1);
}
else {
- emit(without attachment, 1); 
+ emit(without attachment, 1);
}
  }
  }}}
- 
  {{{#!highlight javascript
  // reduce
  function(keys, values) {
 return sum(values);
  }
  }}}
- 
  Using curl you can call it like this:
  
  {{{
- curl -s -i -X POST -H 'Content-Type: application/json' 
+ curl -s -i -X POST -H 'Content-Type: application/json'
-   -d '{map: function(doc){if(doc._attachments) {emit(\with\,1);} else 
{emit(\without\,1);}}, 
+   -d '{map: function(doc){if(doc._attachments) {emit(\with\,1);} else 
{emit(\without\,1);}},
-   reduce: function(keys, values) {return sum(values);}}' 
+   reduce: function(keys, values) {return sum(values);}}'
'http://localhost:5984/somedb/_temp_view?group=true'
  }}}
- 
  In SQL this would be something along the lines of {{{SELECT num_attachments 
FROM table GROUP BY num_attachments}}} (but this would give extra output for 
rows containing more than one attachment).
  
- 
  == Generating a list of unique values ==
- 
  Here we use the fact that the key for a view result can be an array. Suppose 
you have a map that generates (key, value) pairs with many duplicates and you 
want to remove the duplicates. To do so, use {{{emit([key, value], null)}}} as 
the map output.
  
  Call this with ''group=true'' or you only get ''null''.
@@ -95, +81 @@

}
  }
  }}}
- 
  {{{#!highlight javascript
  // reduce
  function(keys, values) {
 return null;
  }
  }}}
+ This will give you results like
  
- This will give you results like
  {{{#!highlight javascript
  {rows:[
  {key:[thisparent,thatlink],value:null},
  {key:[thisparent,thatotherlink],value:null}
  ]}
  }}}
- 
- You can then get all the rows for the key ''thisparent'' with the view 
parameters 
''startkey=[''thisparent]endkey=[thisparent,{}]inclusive_end=false''
+ You can then get all the rows for the key ''thisparent'' with the view 
parameters 
''startkey=[thisparent]endkey=[thisparent,{}]inclusive_end=false''
  
  Note that the trick here is using the key for what you want to make unique. 
You can combine this with the counting above to get a count of duplicate values:
  
@@ -123, +107 @@

}
  }
  }}}
- 
  {{{#!highlight javascript
  // reduce
  function(keys, values) {
 return sum(values);
  }
  }}}
+ If you then want to know the total count for each parent, you can use the 
''group_level'' view parameter: 
''startkey=[thisparent]endkey=[thisparent,{}]inclusive_end=falsegroup_level=1''
- 
- If you then want to know the total count for each parent, you can use the 
''group_level'' view parameter:
- 
''startkey=[''thisparent]endkey=[thisparent,{}]inclusive_end=falsegroup_level=1''
  
  == Get contents of an object with specific attributes e.g. 
doc.objects.[0].attribute ==
- 
  {{{#!highlight javascript
  // map
  function(doc) {
@@ -144, +124 @@

}
  }
  }}}
+ == Arbitrarily query against any document property (uniview) ==
+ '''Note: This is not a generally recommended approach, as your view size