nosql

How to keep null values at the end of sorting in Mongoose? [duplicate]

由 时光总嘲笑我的痴心妄想 提交于 2019-12-25 01:46:11
问题 This question already has an answer here : How can I sort into that nulls are last ordered in mongodb? (1 answer) Closed last year . I am querying a collection and sorting results based on a property. Some documents don't the that property value yet i.e. null. I want to keep the documents with null values at the end of the results after sorting and limiting (asc or desc). Is there a simple way in Mongoose to do that using a single query? If not, how can I use two queries separately since I

What is a Combo Repository and a Service Bus?

由 Deadly 提交于 2019-12-25 01:31:16
问题 I am learning more about NoSQL and specifically DynamoDB. I recently asked this question: Mapping database structure from SQL Server to DynamoDB In the comments under the accepted answer; the answers refers to a Service Bus and a Combo repository. Q1) Is this a Service Bus? (see EventListener class): http://enterprisecraftsmanship.com/2015/05/06/combining-sql-server-and-mongodb-using-nhibernate/ Q2) What is a Combo repository? Is it a "Combination" repository i.e. some methods interface with

手把手 linux下 MongoDB 的使用方法(一）

由 喜你入骨 提交于 2019-12-24 23:16:36
【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> ##1、 创建数据库 语法 use DATABASE_NAME 创建一个 user_data 的数据库，使用 db 命令查看 > use user_data switched to db user_data > db user_data > 查看所有数据库使用show dbs > show dbs admin 0.000GB config 0.000GB local 0.000GB test 0.000GB 可以看到，刚创建的数据库 user_data 并不在数据库的列表中， 要显示它，我们需要向 user_data 数据库插入一些数据。 > db.user_data.insert({"name":"关注公众号，小罗技术笔记，专注于开发技术的研究与知识分享"}) WriteResult({ "nInserted" : 1 }) > show dbs admin 0.000GB config 0.000GB local 0.000GB user_data 0.000GB test 0.000GB MongoDB 中默认的数据库为 test，如果你没有创建新的数据库，集合将存放在 test 数据库中。 ##2、 删除数据库 语法 db.dropDatabase() 以下操作会把user_data数据删除

How to increase a value in Firebase Realtime Database?

由 ε祈祈猫儿з 提交于 2019-12-24 20:13:03
问题 I have this simple struct: { "items": { "item1": { "likes": 4 }, "item2": { "likes": 5 } } } I enable offline mode: Firebase.getDefaultConfig().setPersistenceEnabled(true); Multiple users can increase the "likes" fields at the same time. How can I increase the likes filed by 1 in offline mode? If I get the likes value than set it with the increased value, what happens it the device reaches the server but another users before that have increased the same likes field? Will it overwite the value

Mapping database structure from SQL Server to DynamoDB

由 蓝咒 提交于 2019-12-24 19:54:28
问题 I am thinking about using a NoSQL database to scale database reads. Please see the relational database structure below: CREATE TABLE Person( ID uniqueidentifier not null, Name varchar(100), DateOfBirth datetime) CREATE TABLE Sport ( ID uniqueidentifier not null, Description varchar(50)) -- e.g. Football; Tennis; Badminton etc CREATE TABLE PersonPlaysSport ( PersonID uniqueidentifier FOREIGN KEY REFERENCES Person(ID), SportID uniqueidentifier FOREIGN KEY REFERENCE Sport (ID), primary key

how to wrap xquery results in elements?

由 吃可爱长大的小学妹 提交于 2019-12-24 19:42:59
问题 How do I wrap each result in a <book_result> element? the xquery itself: <new_cat>{ for $x in catalog/book order by $x/title return ($x/title, $x/author) }</new_cat> which runs fine, but the title and author aren't wrapped in a new book: thufir@dur:~/basex/microsoft$ thufir@dur:~/basex/microsoft$ basex -i w3school_data title_author.xq <new_cat> <title>Creepy Crawlies</title> <author>Knorr, Stefan</author> <title>Lover Birds</title> <author>Randall, Cynthia</author> <title>MSXML3: A

MongoDB: upsert with different values for update and insert

由 旧时模样 提交于 2019-12-24 19:08:59
问题 A little context: I have a document for each user that contains an array with latest 20 events related to a user. As MongoDB does not have this feature(to cap arrays inside a document), I will push my event and pop the latest one. My problem: initializing the document(aka filling array with nulls). I want to atomically: create document containing an array with 20 null values and push one value, if document does not exist or update document (push one value in array), if document exists Do you

Database table design with duplication of data

由 主宰稳场 提交于 2019-12-24 18:43:45
问题 I was having some problem when trying to design for my firebase database structure. Basically, 1 account can have many receipts, 1 receipts can have many items. Here is the JSON: receipts { accountID1 : { receiptID1 : { date : "07/07/2017" store : { storeName : "store1" storeAddr : "addr1" } currency : { currencyName : "currency1" currentcySymbol : "$" } totalAmount : "50.00" items : { itemID1 : true, itemID2 : true, } } receiptID2 : { date : "08/07/2017" store : { storeName : "store1"

Amazon DynamoDB - Designing tables based on friendships

由 蓝咒 提交于 2019-12-24 18:01:09
问题 In my test project, I'm trying to simulate a small social network that allows the users to post a personal status message. I would to use DynamoDB for status message and MySQL for the user friendships. My doubt is: how can I design my dynamo table to store status message and fetch only the status of friends users? For example, I need to fetch all the statuses of my friends ordered by creation date from Dynamo. I've thought of a table with this indexes: HashKey : user_id RangeKey: creation

Cassandra Schema Design

由 我们两清 提交于 2019-12-24 16:48:42
问题 I'm continuing exploring Cassandra and I would like to create Student <=> Course relation which is similar to Many-to-Many on RDBMS. In term of Queries I will use the following query; Retrieve all courses in which student enrolled. Retrieve all students enrolled in specific course. Let's say that I create to Column Families. one for Course and another for Student. CREATE COLUMN FAMILY student with comparator = UTF8Type AND key_validation_class=UTF8Type and column_metadata=[ {column_name
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