Final Exam Flashcards

Question

What are the basic data types in MongoDB?

Answer 1

MongoDB supports a wide range of data types as values in documents. Documents in MongoDB are similar to objects in JavaScript. Along with JSON’s essential key/value–pair nature, MongoDB adds support for a number of additional data types. The common data types in MongoDB are:- Null {"x" : null} Boolean {"x" : true} Number {"x" : 4} String {"x" : "foobar"} Date {"x" : new Date()} Regular expression {"x" : /foobar/i} Array {"x" : ["a", "b", "c"]} Embedded document {"x" : {"foo" : "bar"}} Object ID {"x" : ObjectId()}

Answer 2

You should use MongoDB when you are building internet and business applications that need to evolve quickly and scale elegantly. MongoDB is popular with developers of all kinds who are building scalable applications using agile methodologies. MongoDB is a great choice if one needs to: Support a rapid iterative development. Scale to high levels of read and write traffic - MongoDB supports horizontal scaling through Sharding, distributing data across several machines, and facilitating high throughput operations with large sets of data. Scale your data repository to a massive size. Evolve the type of deployment as the business changes. Store, manage and search data with text, geospatial, or time-series dimensions.

Answer 3

Generally, NoSQL is preferred for: Graph or hierarchical data Data sets which are both large and mutate significantly, Businesses growing extremely fast but lacking data schemata. In terms of use cases, this might translate to social networks, online content management, streaming analytics, or mobile applications. SQL is more appropriate when the data is: Small Conceptually modeled as tabular In systems where consistency is critical.

Answer 4

SQL has been around for over 40 years, so it is recognizable, documented, and widely-used. Safe and versatile, it’s particularly well suited for complex queries. However, SQL restricts the user to working within a predefined tabular schema, and more care must be taken to organize and understand the data before it is used. The dynamic schemata of NoSQL databases allow representation of alternative structures, often alongside each other, encouraging greater flexibility. There is less emphasis on planning, greater freedom when adding new attributes or fields, and the possibility of varied syntax across databases. As a group, however, NoSQL languages lack the standard interface which SQL provides, so more complex queries can be difficult to execute. Though there are many dialects of SQL, all share a common syntax and almost-identical grammar. When querying relational databases, fluency in one language translates to proficiency in most others. On the other hand, there is very little consistency between NoSQL languages, as they concern a diverse set of unrelated technologies. Many NoSQL databases have a unique data manipulation language constrained by particular structures and capabilities.

Answer 5

Most SQL databases can be scaled vertically, by increasing the processing power of existing hardware. NoSQL databases use a master-slave architecture which scales better horizontally, with additional servers or nodes. These are useful generalizations, but it’s important to note: SQL databases can be scaled horizontally as well, though sharding or partitioning logic is often the user’s onus and not well supported. NoSQL technologies are diverse and while many rely on the master-slave architecture, options for scaling vertically also exist. Savings made using more efficient data structures can overwhelm differences in scalability; most important is to understand the use case and plan accordingly.

Answer 6

SQL database schemata always represent relational, tabular data, with rules about consistency and integrity. They contain tables with columns (attributes) and rows (records), and keys have constrained logical relationships. NoSQL databases need not stick to this format, but generally fit into one of four broad categories: Column-oriented databases transpose row-oriented RDBMSs, allowing efficient storage of high-dimensional data and individual records with varying attributes. Key-Value stores are dictionaries which access diverse objects with a key unique to each. Document stores hold semi-structured data: objects which contain all of their own relevant information, and which can be completely different from each other. Graph databases add the concept of relationships (direct links between objects) to documents, allowing rapid traversal of greatly connected data sets.

Answer 7

SQL databases must follow the "ACID" properties: - Atomicity: transactions must either succeed completely or fail completely, even if there is a system failure. - Consistency: the database must follow rules to prevent corruption and maintain its integrity. - Isolation: concurrent transactions should not affect each other, and their final result should be the same as if they were run sequentially. - Durability: successful transactions must be permanent, even if there is a system failure. NoSQL databases follow the "CAP" theorem, which means they can only guarantee two out of three properties: - Consistency: all requests receive the latest result or an error. - Availability: all requests get a response, regardless of the result's recency. - Partition tolerance: the system can continue to operate despite delays or losses between nodes. In summary, SQL databases ensure transactional integrity, while NoSQL databases prioritize scalability and availability.

Answer 8

SQL databases represent massive communities, stable codebases, and proven standards. Multitudes of examples are posted online and experts are available to support those new to programming relational data. NoSQL technologies are being adopted quickly, but communities remain smaller and more fractured. However, many SQL languages are proprietary or associated with large single-vendors, while NoSQL communities benefit from open systems and concerted commitment to onboarding users. SQL is available to most major platforms, from operating systems to architectures and programming languages. Compatibility varies more widely for NoSQL, and dependencies need to be investigated more carefully.

Answer 9

mongoose is an object modeling package for Node that essentially works like an ORM.

Answer 10

Mongoose provides a straight-forward, schema-based solution to model your application data. It includes built-in type casting, validation, query building, business logic hooks and more, out of the box. It is a Object Document Mapper or ODM. An Object Modelling Tool. However, if our collection contains documents with an uncertain schema, the MongoDB driver is the most straightforward alternative. It allows for more flexibility as one can directly interact with the database.

Answer 11

Similarly to a relational database, MongoDB allows you to use schemas to define the fields and data types within your collections. One of the powerful schema options available in MongoDB is to relate documents to one another, either via embedding or referencing. Embedded documents are stored as children inside a parent document. This means they are all stored under one collection, and whenever you retrieve the parent document, you also retrieve all its embedded documents. Unlike embedded documents, referenced documents are stored in a separate collection to their parent document. Therefore, it’s possible to retrieve the parent document without retrieving any of its referenced documents. In storing the addresses of the child documents e.g. via a linked field using references.

Answer 12

npm install mongoose

Answer 13

When we do "npm install", then it install the modules. If we need to update the version of module in package.json, then we have to do it manually. BUT when we do "npm install --save", then it install the modules and update the package.json automatically.

Answer 14

package.json is a versioning file used to install multiple packages in your project. package.json file contains metadata about the project and also the functional dependencies that is required by the application. package.lock.json is created for locking the dependency with the installed version. Without package.lock.json, there might be some differences in installed versions in different environments.

Answer 15

Dependencies are modules your project depends on, devDependencies are modules you use to develop your project. Examples of dependencies are request, through2 and concat-stream. Examples of devDependencies are grunt, mocha, eslint, tape, and browserify.

Answer 16

missing package.json

Answer 17

//include the js library var mongoose = require('mongoose'); //establish database connection mongoose.connect('mongodb://localhost:27017/mongodb'); //Create schema var userSchema = mongoose.Schema({ name: String, //datatype is string username: { type: String, required: true, unique: true }, //type is string and its required field and its unique password: { type: String, required: true }, admin: Boolean, location: String, created_at: Date //datatype of date }); //create User Object var User = mongoose.model('User', userSchema); //Save User details in database var userDetails = new User({ name: 'Test user',username:'testuser',password:'test12@',location:'mohali' }); userDetails.save(function (err) {if (err) console.log ('Error on save!')}); console.log(userDetails);

Answer 18

Asynchronous programming uses an event loop to run the program. When a task needs to be performed, it's started, and the code keeps running without waiting for the result. Once the result is ready, an event is triggered, and the program continues executing the code from the event handler. This allows a single thread to handle multiple tasks at once.

Answer 19

An async function always returns a promise. The await still has to wait for the promise to resolve: a pending promise gets returned when we call getData() in order to set data equal to it. If we wanted to get access to the resolved value "I made it", we could have used the .then() method on data: data.then(res ⇒ console.log(res))` This would’ve logged "I made it!"". The correct answer is C.

Answer 20

Advantages: promise can solve callback hell, which greatly enhances the readability and maintainability of nested functions, Disadvantages: unable to cancel promise, errors need to be captured by callback function; If the callback function is not set, the error thrown by promise will not be reflected to the outside; When it is in the pending state, it is impossible to know which stage it has reached, whether it has just started or is about to complete

Answer 21

The asynchronous function requires callbacks as a return parameter. When multiple asynchronous functions are chained together then callback hell situation comes up.

Answer 22

Virtual DOM: It uses virtual DOM similar to other existing frameworks such as ReactJS, Ember etc. Virtual DOM is a light-weight in-memory tree representation of the original HTML DOM and updated without affecting the original DOM. Components: Used to create reusable custom elements in VueJS applications. Templates: VueJS provides HTML based templates that bind the DOM with the Vue instance data Routing: Navigation between pages is achieved through vue-router Light weight: VueJS is light weight library compared to other frameworks.

Answer 23

Lifecycle hooks are a window into how the library you’re using works behind-the-scenes. By using these hooks, you will know when your component is created, added to the DOM, updated, or destroyed.

Answer 24

1 - App.vue This is typically the root of your application defined in Vue Component file format. It’s usually something that defines the template for your page. 2 - main.js This is usually the JavaScript file that will initialize this root component into a element on your page. It is also responsible for setting up plugins and 3rd party components you may want to use in your app. 3 - router folder may contain the index.js file which contains all the router configurations. 4 - views folder contains components that are related to different views 5 - contains all other components (*.vue files) 6 - the assets folder contains images, css etc. that are used by components

Answer 25

Directives are instruction for VueJS to do things in a certain way. Essentially, a directive is some special token in the markup that tells the library to do something to a DOM element

Answer 26

VueJS provides set of directives to show or hide elements based on conditions. The available directives are: v-if, v-else, v-else-if and v-show v-if: The v-if directive adds or removes DOM elements based on the given expression. For example, the below button will not show if isLoggedIn is set to false. You can also control multiple elements with a single v-if statement by wrapping all the elements in a

Final Exam Flashcards

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