MongoDB – walk-through – (Part 1)

MongoDB is an open-source document database that provides high performance, high availability, and automatic scaling. MongoDB obviates (remove a need or difficulty) the need for an Object Relational Mapping (ORM) to facilitate development.

Download RoboMongo Here: https://robomongo.org/

Install MongoDB for Windows

MongoDB requires a data directory to store all data. MongoDB’s default data directory path is \data\db.

Create a configuration file. The file must set systemLog.path. Include additional configuration options as appropriate.

For example, create a file at C:\mongodb\mongod.cfg that specifies both systemLog.path and storage.dbPath:

Install the MongoDB service by starting mongod.exe with the –install option and the -config option to specify the previously created configuration file.

Starting and stopping the service

Mongoimport

mongoimport –db test –collection restaurants –drop –file primer-dataset.json

Help command section

Insert document

All queries in MongoDB have the scope of a single collection. This means you can only return result from a single collection (list of documents).

Query by a Field in an Embedded Document

Query by a Field in an Array

Greater Than Operator ($gt)

You can specify a logical conjunction (AND) for a list of query conditions by separating the conditions with a comma in the conditions document.

You can specify a logical disjunction (OR) for a list of query conditions by using the $or query operator.

To specify an order for the result set, append the sort() method to the query.

You can use the update() method to update documents of a collection. The method accepts as its parameters:

  • a filter document to match the documents to update,
  • an update document to specify the modification to perform, and
  • an options parameter (optional).

Some update operators, such as $set, will create the field if the field does not exist.

Update an Embedded Field

To update a field within an embedded document, use the dot notation. When using the dot notation, enclose the whole dotted field name in quotes.

By default, the update() method updates a single document. To update multiple documents, use the multi option in the update() method.

To replace the entire document except for the _id field, pass an entirely new document as the second argument to the update() method.

After the following update, the modified document will only contain the _id field, name field, the addressfield.
i.e. the document will not contain the restaurant_id, cuisine, grades, and the borough fields.

If no document matches the update condition, the default behavior of the update method is to do nothing. By specifying the upsert option to true, the update operation either updates matching document(s) or inserts a new document if no matching document exists.

To specify a remove condition, use the same structure and syntax as the query conditions.

By default, the remove() method removes all documents that match the remove condition. Use the justOne option to limit the remove operation to only one of the matching documents.

Remove All Documents

To remove all documents from a collection, pass an empty conditions document {} to the remove() method.

 

Drop a Collection

To remove all documents from a collection, it may be more efficient to drop the entire collection, including the indexes, and then recreate the collection and rebuild the indexes. Use the drop() method to drop a collection, including any indexes.

In MongoDB, write operations are atomic on the level of a single document. If a single remove operation removes multiple documents from a collection, the operation can interleave with other write operations on that collection.

So the transactions are interleaved, means second transaction is started before the first one could end. And execution can switch between the transactions back and forth. It can also switch between multiple transactions.

This could actually cause inconsistency in the system. But they are handled by the database systems.

MongoDB must perform a collection scan, i.e. scan every document in a collection, to select those documents that match the query statement. If an appropriate index exists for a query, MongoDB can use the index to limit the number of documents it must inspect.

To create an index on a field or fields, pass to the createIndex() method an index key specification document that lists the fields to index and the index type for each field:

  • For an ascending index type, specify 1 for <type>.
  • For a descending index type, specify -1 for <type>.

Create an ascending index on the "cuisine" field of the restaurants collection.

Compound indexes which are indexes on multiple fields.

Drivers for MongoDB are the client libraries that handle the interface between the application and the MongoDB servers and deployments. Drivers are responsible for managing connections to MongoDB standalone instances, replica sets, or sharded clusters. Drivers provide the methods and interfaces that applications use to interact with MongoDB as well as handle the translation of documents between BSON objects and native mapping structures.

The advantages of using documents are:

  • Documents (i.e. objects) correspond to native data types in many programming languages.
  • Embedded documents and arrays reduce need for expensive joins.
  • Dynamic schema supports fluent polymorphism.

MongoDB’s replication facility, called replica set, provides:

  • automatic failover and
  • data redundancy.

A replica set is a group of MongoDB servers that maintain the same data set, providing redundancy and increasing data availability.

MongoDB provides horizontal scalability as part of its core functionality:

  • Sharding distributes data across a cluster of machines.
  • Tag aware sharding allows for directing data to specific shards, such as to take into consideration geographic distribution of the shards.

If a collection does not exist, MongoDB creates the collection when you first store data for that collection.

MongoDB provides the db.createCollection() method to explicitly create a collection with various options, such as setting the maximum size or the documentation validation rules. If you are not specifying these options, you do not need to explicitly create the collection since MongoDB creates new collections when you first store data for the collections.

Starting in MongoDB 3.2, however, you can enforce document validation rules for a collection during update and insert operations.

Capped collections are fixed-size collections that support high-throughput operations that insert and retrieve documents based on insertion order. Capped collections work in a way similar to circular buffers: once a collection fills its allocated space, it makes room for new documents by overwriting the oldest documents in the collection.

cap
1. put a lid or cover on.
“he capped his pen”
2. place a limit or restriction on (prices, expenditure, or other activity).
“council budgets will be capped”
synonyms: set a limit on, limit, restrict.

Consider the following potential use cases for capped collections:

  • Store log information generated by high-volume systems. Inserting documents in a capped collection without an index is close to the speed of writing log information directly to a file system. Furthermore, the built-in first-in-first-out property maintains the order of events, while managing storage use.
  • Cache small amounts of data in a capped collections. Since caches are read rather than write heavy, you would either need to ensure that this collection always remains in the working set (i.e. in RAM) or accept some write penalty for the required index or indexes.

If you plan to update documents in a capped collection, create an index so that these update operations do not require a collection scan. If an update or a replacement operation changes the document size, the operation will fail. That’s why try to use capped collections for write-and-forget type storage. Like error logs and cache that you will not possibly update the document over time.

You cannot delete documents from a capped collection. To remove all documents from a collection, use the drop() method to drop the collection and recreate the capped collection. You cannot shard a capped collection.

Use natural ordering to retrieve the most recently inserted elements from the collection efficiently. This is (somewhat) analogous to tail on a log file.
You must create capped collections explicitly using the db.createCollection() method.

You may also specify a maximum number of documents for the collection using the max field as in the following document. The size argument is always required, even when you specify max number of documents. MongoDB will remove older documents if a collection reaches the maximum size limit before it reaches the maximum document count.

If you perform a find() on a capped collection with no ordering specified, MongoDB guarantees that the ordering of results is the same as the insertion order.

To retrieve documents in reverse insertion order:

Use the isCapped() method to determine if a collection is capped, as follows:

You can convert a non-capped collection to a capped collection with the convertToCapped command:

This command obtains a global write lock and will block other operations until it has completed.

For additional flexibility when expiring data, consider MongoDB’s TTL indexes, as described in Expire Data from Collections by Setting TTL. These indexes allow you to expire and remove data from normal collections using a special type, based on the value of a date-typed field and a TTL value for the index.

TTL Collections are not compatible with capped collections.

BSON con­tains ex­ten­sions that al­low rep­res­ent­a­tion of data types that are not part of the JSON spec. For ex­ample, BSON has a Date type and a BinData type.

Documents have the following restrictions on field names:

  • The field name _id is reserved for use as a primary key; its value must be unique in the collection, is immutable, and may be of any type other than an array.
  • The field names cannot start with the dollar sign ($) character.
  • The field names cannot contain the dot (.) character.
  • The field names cannot contain the null character.

The maximum BSON document size is 16 megabytes.

To store documents larger than the maximum size, MongoDB provides the GridFS API.

You can access the creation time of the ObjectId, using the ObjectId.getTimestamp() method.

BSON strings are UTF-8. UTF-8 is a character encoding capable of encoding all possible characters, or code points, defined by Unicode. The encoding is variable-length and uses 8-bit code units.

The BSON timestamp type is for internal MongoDB use. For most cases, in application development, you will want to use the BSON date type.

BSON Date is a 64-bit integer that represents the number of milliseconds since the Unix epoch (Jan 1, 1970). This results in a representable date range of about 290 million years into the past and future. BSON Date type is signed. Negative values represent dates before 1970.

var mydate2 = ISODate() will equivalent below;

 

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