nosql

问题 Hi I am a newbie to Firebase .This is how my data looks like I would like to know how I can retrieve the distributorInfo from retailers.I am trying to retrieve distributorInfo from a FirebaseRecyclerAdapter's populateViewHolder method.I am able to get the key for the selected item.How do I get the information inside distributorInfo? private void getRetailers() { FirebaseRecyclerAdapter<RetailerInfo,RetailerViewHolder> adapter = new FirebaseRecyclerAdapter<RetailerInfo, RetailerViewHolder>(

问题 New to Meteor and MongoDB, coming from a relational database background. This question actually reflects my puzzle at how relations are handled in MongoDB. Example: I want to insert a recipe into a collection of recipes, which in this case is a comma delimited string of multiple ingredients. I want, however, to insert these ingredients into a collection of ingredients at the same time. And I would like to have the recipe refer to the ingredients in the ingredients collection, so that, say, if

问题 I have 5 collections - A, B, C, D, E. I have a document which is stored in A, and related to documents in the other 4 collections. I am using MeteorJS. Now, I have to delete the data in the document safely. In other words, the document has to be deleted in A, as well as its references in the others. Only after they are all removed, I have to show the user a success message. Right now, I have only: A.remove(documentID); I have to use a callback here to show the user the result. I am completely

问题 I'm newbie to the orientdb, I'm using netbeans's (add new connection wizard) to add a connection to the orientdb, I used orientdb-jdbc-2.0.2-all.jar as a jdbc driver, but I got the following error after clicking on test connection Snapshot of the error I made sure that the database is connected and everything is right, any idea? 回答1: The URL should be jdbc:orient:remote:localhost/Sensor_Data Look at the documentation: http://www.orientechnologies.com/docs/last/orientdb-jdbc.wiki/Home.html

问题 I have a scenario that I have a document inside which I have a sub collection. Now, I want to modify/update one of the sub document from the sub collection. I want to match the parent document and the sub document first before modifying the sub document. I am using mongoose/node.js and MongoDB Here is my schema:- var mongoose = require('mongoose'); var Schema = mongoose.Schema; var HostSchema = new Schema({ aid : String, cars : [{ carid : String, status_code: Number }] }); module.exports =

问题 Two questions: If I remove all the data inside a collection (db.mycollection.remove({})) will the indexing information I created previously be lost? How often (how many more entries must I have) should I recreate the index? 回答1: Calling remove() will remove the indexed data but not the indexes themselves (dropping a collection will do that). So when you insert new documents they will be added to the indexes you created prior to the remove() call. You don't need to recreate the index. Once you

问题 I have 2 main nodes in my database: Users and Projects . Each user can be assigned to multiple projects, in different roles. After reading about how to structure many to many relationship, I ended up that it should look like this: users : { user1 : { name : blah, email : a@a.com, projects : { projects1key : true, projects2key : true } } } projects : { project1key : { name : blahserve, category : blahbers, providers : { user1 : true, user7 : true } } } What I couldn't figure out is how I can

问题 I call the Elements with find() method and after than i want to update all. For example: db.collection.find().limit(10).update({$set: {'column' : 'value'}}); how can i fix this? 回答1: If you want to apply update to every document in collection, use {multi:true} option db.collection.update({},{$set: {'column' : 'value'}},{multi:true}); For more detail, see collection.update However, if you want to update selected number of documents, you'll be taking longer route. db.collection.find().limit(10)

问题 As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. Closed 7 years ago . I'm currently writing a webapp in Ruby on Rails that matches users based on questions they answered. Then they can search for a range

问题 I'm using RethinkDB driver for Java. I want to filter the rows without field endedAt in table jam like this: public List<Jam> getCurrent(){ Cursor cursor = r.table("jam") .filter(row -> row.hasFields("endedAt")).not() .run(conn); List<Map<String,Object>> list=cursor.toList(); return list.stream().map(item->JamRepository.toJam(item)).collect(Collectors.toList()); } And I've got this error Expected type DATUM but found SELECTION Java I have another filter function in another class: public List