(MongoDB Full Text Search)
Hello,
I have put some fields in index and this is how I could search for a search_keyword.
BasicDBObject search = new BasicDBObject("$search", "search_keyword");
BasicDBObject textSearch = new BasicDBObject("$text", search);
DBCursor cursor = users.find(textSearch);
I don't want search_keyword to be searched in all the fields specified in the index. *Is there any method to specify search_keyword to be searched in specific fields from the index??*
If so, please give me some idea how to do it in Java.
Thank you.
If you want to index a single field and search for it then it is the way it works by default. Lets say you want to index the field companyName. When you perform $text search on this collection, only the data from the companyName field will be used because you only included that field in your index.
Now the second scenario, your $text index includes more than one field. In this case you cannot limit the search to only look for values indexed from a specific field. The $text index is constructed on the collection level and a collection can have at most one $text index. Your option to limit search on specific field in this case may be to use regex instead.
MongoDB has the flexibility to fulfil requirements of other scenarios, but you can also evaluate using other technologies if your application is heavily search-driven and you are primarily after a full-text search engine for locating documents by keyword with a rich query syntax. ElasticSearch might be an alternative here. It really depends on the type of the application and your needs.
Related
Currently, I have a MongoDB instance, which contains a collection with a lot of entities. Each entity contains a string attribute, which represents some text. My goal is to provide a strict text search in the collection. It should work as a MySQL query:
SELECT *
FROM texts
WHERE text LIKE '%test%';
MongoDB text index would be great, but it doesn't provide a strict search. How I could organize a strict search for such data? Could I do some optimization?
I already checked other software (such as ElasticSearch, Lucene, MongoDB, ClickHouse), but I haven't found options to do it. Searching as now took too much time.
In mongoDB you can do it as follow:
db.texts.find({ text:/test/ })
Since it is not possible to find "blueberry" by the word "blue" by using a mongodb full text search, I want to help my users to complete the word "blue" to "blueberry". To do so, is it possible to query all the words in a mongodb full text index -> that I can use the words as suggestions i.e. for typeahead.js?
Language stemming in text search uses an algorithm to try to relate words derived from a common base (eg. "running" should match "run"). This is different from the prefix match (eg. "blue" matching "blueberry") that you want to implement for an autocomplete feature.
To most effectively use typeahead.js with MongoDB text search I would suggest focusing on the prefetch support in typeahead:
Create a keywords collection which has the common words (perhaps with usage frequency count) used in your collection. You could create this collection by running a Map/Reduce across the collection you have the text search index on, and keep the word list up to date using a periodic Incremental Map/Reduce as new documents are added.
Have your application generate a JSON document from the keywords collection with the unique keywords (perhaps limited to "popular" keywords based on word frequency to keep the list manageable/relevant).
You can then use the generated keywords JSON for client-side autocomplete with typeahead's prefetch feature:
$('.mysearch .typeahead').typeahead({
name: 'mysearch',
prefetch: '/data/keywords.json'
});
typeahead.js will cache the prefetch JSON data in localStorage for client-side searches. When the search form is submitted, your application can use the server-side MongoDB text search to return the full results in relevance order.
A simple workaround I am doing right now is to break the text into individual chars stored as a text indexed array.
Then when you do the $search query you simply break up the query into chars again.
Please note that this only works for short strings say length smaller than 32 otherwise the indexing building process will take really long thus performance will be down significantly when inserting new records.
You can not query for all the words in the index, but you can of course query the original document's fields. The words in the search index are also not always the full words, but are stemmed anyway. So you probably wouldn't find "blueberry" in the index, but just "blueberri".
Don't know if this might be useful to some new people facing this problem.
Depending on the size of your collection and how much RAM you have available, you can make a search by $regex, by creating the proper index. E.g:
db.collection.find( {query : {$regex: /querywords/}}).sort({'criteria': -1}).limit(limit)
You would need an index as follows:
db.collection.ensureIndex( { "query": 1, "criteria" : -1 } )
This could be really fast if you have enough memory.
Hope this helps.
For those who have not yet started implementing any database architecture and are here for a solution, go for Elasticsearch. Its a json document driven database similar to mongodb structurally. It has "edge-ngram" analyzer which is really really efficient and quick in giving you did you mean for mis-spelled searches. You can also search partially.
I am trying to run a query on Lucene .NET 2.9.2 index without any luck:
My index holds documents, some of them contain numeric field called "MyNum" and some of them are not.
The field is indexed.
I am trying to count the total documents that contain the field, no matter the fields value.
Could some one please help me out?
A query like fieldX:* should return all of the documents that contain field "fieldX".
You may need to allow for a prefixed * in your search (I don't have a copy of Lucene up at the moment.)
You may use the wildcard query to retrieve all documents with specific field. Just provide the * as value (this is just regular wildcard). Here is the sample code:
IndexSearcher searcher = new IndexSearcher(reader);
TopDocs docs = searcher.Search(new WildcardQuery(new Term("MyNum", "*")), int.MaxValue);
Console.WriteLine(docs.TotalHits);
This question already has answers here:
How to query MongoDB with "like"
(45 answers)
Closed 7 years ago.
Is there in MongoDB/mongoose 'like' statement such as in SQL language?
The single reason of using is a implementation of full-text searching.
MongoDB supports RegularExpressions.
Two ways we can implement regular expression using java API for mongodb:
Expression 1:
I need to search start with that string in document field
String strpattern ="your regular expression";
Pattern p = Pattern.compile(strpattern);
BasicDBObject obj = new BasicDBObject()
obj.put("key",p);
Example : (consider I want to search wherever name start with 'a')
String strpattern ="^a";
Pattern p = Pattern.compile(strpattern);
BasicDBObject obj = new BasicDBObject()
obj.put("name",p);
Expression 2:
I need to search multiple words in one field , you can use as follows
String pattern = "\\b(one|how many)\\b";
BasicDBObject obj = new BasicDBObject();
//if you want to check case sensitive
obj.put("message", Pattern.compile(pattern,Pattern.CASE_INSENSITIVE));
Although you can use regular expressions, you won't get good performance on full text search because a contains query such as /text/ cannot use an index.
A begins-with query such as /^text/ can, however, use an index.
If you are considering full text search on any large scale please consider MongoDB's Multi Key Search feature.
Update
As of MongoDB v3.2 you can also use a text index.
Consider making a script at application level that transforms your data to tokens (words). Then treat tokens as tags, build an index on those tokens, and then search the tokens like searching for tags. This is like creating an inverted index.
For way better search capabilities on text consider using Lucene instead of MongoDB.
Use regex: /^textforesarc$/i. Just don't forget to say goodbye to performance :).
Simulating regex search with like will not hit custom defined index. Only starts with is supported for now.
I have the following query (MongoMapper/Rails):
Card.where(:card_tags => {:$all => search_tags}
Where card_tags is an array of string tags and search_tags is in array of the search strings. At the moment if someone searches 'snow', no results with tag 'snowboarding' will be returned.
How can I modify this query to search whether any strings in card_tags contains any of the strings in search_tags? Regular expressions come to mind but not sure of the syntax given these are arrays...
Thanks
You can use regular expressions but you will be doing full collection scans - this is going to be bad for performance.
You can use regex with an index only if you "starts with" type of searches, but I doubt you want to limit yourself to that.
For fulltext searching, you are better off using some external search service for this - like Lucene, ElasticSearch, or Solr.
Refer to this post too: like query in mongoDB