bson | 易学教程

How to get ordered dictionaries in pymongo?

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问题 I am trying get ordered dictionaries in Pymongo. I have read it can be done with bson.son.Son. The Docs are Here However, I can't seem to make it work. There is not much on google about it. There are some discussions on configuring pymongo first to tell it to use SON objects but no examples. A friend suggested passing a param when you do a find. He couldn't remember. I'm able to create the SON objects. But when they get inserted into the DB and then come back out they are just plain dicts. I

Mongo初学

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 关系型数据库与MongoDB区别： SQL MongoDB 解释/说明 database database 数据库 table collection 数据库表/集合 row document 数据记录行/文档 column field 数据字段/域 index index 索引 table joins 表连接，MongoDB不支持 primary key primary key 主键，MongoDB自动将_id字段设置为主键数据库：不能是空字符串（“”）不得含有（空格）、$、/、\ 和空字符（‘’）应全部小写最多64个字节文档（Document）注意：文档中的键/值对是有序的文档中的值不仅可以是在双引号里面的字符串，还可以是其他几种数据类型（甚至可以是整个嵌入的文档） MongoDB区分类型和大小写 MongoDB的文档不能有重复的键文档的键是字符串。除了少数例外情况，键可以使用任意UTF-8字符。文档命名规则：键不能含有空字符。这个字符用来表示键的结尾。 .和$有特别的意义，只有在特定的环境下才能使用。以下划线“_”开头的键是保留的（不是严格要求的）集合（collection）集合命名规则：集合名不能是空字符串“”。集合名不能含有空字符，这个表示集合的结尾。集合名不能以

How can I get JSON from BSON without my keys all being named “Key”?

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问题 I'm trying to read from a database and then return the result to the user as json. What's happening is that I'm getting output like: [{"Key":"foo","Value":"bar"}] When I would like to get: "{"foo":"bar"}" How do I get the former? Example: (reading from the db and converting Raw to string are not shown) package main import ( "encoding/json" "fmt" "go.mongodb.org/mongo-driver/bson" ) func main() { var data = "{\"foo\":\"bar\"}" var testInterface interface{} e := bson.UnmarshalExtJSON([]byte

How can I get JSON from BSON without my keys all being named “Key”?

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mongodb BSON size

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问题 There is post on stackoverflow in which it is mentioned that BSON size limit is upto 4MB or 8MB. Well for my application the JSON documents would be hardly few tens of kilobytes or even less. Is mongodb suitable for my application if my document size is so less. What I actually want to ask is, do mongodb set aside 4 MB or 8 MB of space for every document so as to improve quick lookups. Well the question might sound stupid, but can anyone tell is it suitable for my application or not. 回答1: No,

MongoDB Java driver: Undefined values are not shown

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问题 Open mongo shell and create a document with a undefined value: > mongo MongoDB shell version: 2.4.0 connecting to: test > use mydb switched to db mydb > db.mycol.insert( {a_number:1, a_string:"hi world", a_null:null, an_undefined:undefined} ); > db.mycol.findOne(); { "_id" : ObjectId("51c2f28a7aa5079cf24e3999"), "a_number" : 1, "a_string" : "hi world", "a_null" : null, "an_undefined" : null } As we can see, javascript translates the "undefined" value (stored in the db) to a "null" value, when

Complex query with two $OrderBy

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问题 Here's the structure part of my collection : by: [ { id: ObjectId("XX"), type: NumberInt(1) } ], timestamp: NumberInt(), // is timestamp 1 status: NumberInt(0), mails: [ { id: ObjectId("YY"), text: "", timestamp: NumberInt(), // is timestamp 2 } ] I can recover my data in chronological order according to the timestamp 1 via the following lines: ... bson_init(&query); bson_append_document_begin(&query, "$orderby", -1, &child); bson_append_int32(&child, "timestamp", -1, 1); bson_append_document

Why the bson java implementation uses 4 bytes inc field?

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问题 In BSON Java implementation, an ObjectId is composed by 3 pieces (source code: http://grepcode.com/file/repo1.maven.org/maven2/org.mongodb/mongo-java-driver/2.9.0/org/bson/types/ObjectId.java#ObjectId.%3Cinit%3E%28int%2Cint%2Cint%29 ): XXXX XXXX XXXX ------------------------- time machine&pid inc (each X represents a byte) this is a bit different from what's described in document (doc: http://docs.mongodb.org/manual/core/object-id/ ) XXXX XXX XX XXX -------------------------- time machine pid

How to resolve null data on Observable Collection to data grid binding?

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问题 I've set up a database on MongoLab that is queried and parsed to a Model. The collection in that model is in turn bound to the data grid. But when I query the database, the only data showing on the grid is the object ID for the document. In order to debug the issue I initialized the list with constant data for each field, and the binding works, filling each field on the grid. Which then lead me to check how I'm mapping the data to the Model. I then stepped through the contents of the

Exception in thread “main” java.lang.IllegalArgumentException: invalid ObjectId [7887978]

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问题 I am really facing challenge in changing String object to ObjectId using BSON API. The error I am facing: Exception in thread "main" java.lang.IllegalArgumentException: invalid ObjectId [7887978] at org.bson.types.ObjectId.<init>(ObjectId.java:130) at org.bson.types.ObjectId.<init>(ObjectId.java:124) at com.sample.common.Main.main(Main.java:8) The simple code below for reference: import org.bson.types.ObjectId; public class Main { public static void main(String[] args) { String number =