Merge aa488b84d3 into 10872e02d1

databases/mongoose.js

@@ -0,0 +1,245 @@
+/* *****************************************************************
+ * Mongoose is a MongoDB object modeling tool designed to work in an asynchronous environment.
+ * Mongoose supports both promises and callbacks.
+ * ****************************************************************/
+
+// Import Mongoose
+const mongoose = require("mongoose");
+
+/* *****************************************************************
+    List of Mongoose Data Types:
+        String
+        Number
+        Date
+        Buffer
+        Boolean
+        Mixed
+        ObjectId
+        Array
+        Decimal128
+        Map
+        Schema
+        UUID
+    ******************************************************************/
+
+/* *****************************************************************
+ * Schema
+ * A schema is a blueprint for a model.
+ * It defines the structure of the document, default values, validators, etc.
+ * ****************************************************************/
+
+// Define schema for the a collection
+const productSchema = new mongoose.Schema({
+  name: {
+    type: String,
+    immutable: true, // This field cannot be changed after creation
+  },
+  price: {
+    type: Number,
+    min: 0, // Minimum value is 0
+    max: 10000, // Maximum value is 10000
+    required: true, // Not specifying a required field will result in validation error
+  },
+  category: {
+    type: String,
+    enum: ["fruit", "vegetable", "dairy"], // Only these values are allowed for 'category'
+  },
+  tags: [
+    // Array of String
+    {
+      type: String,
+      minLength: 2, // Minimum length of a single tag is 2
+      maxlength: 10, // Maximum length of a single tag is 10
+    },
+  ],
+  createdAt: {
+    type: Date,
+    // WRONG!
+    // default: Date.now(), // This results in the current date being set (as a static value) when the schema is compiled
+
+    // Correct!
+    default: () => Date.now(), // We instead use a getter function that returns the current date when called
+  },
+});
+
+// Create a model from the schema
+const Product = mongoose.model("Product", productSchema);
+// We can now use the model to create new documents in the 'products' collection
+
+/* *****************************************************************
+ * Promises
+ * ****************************************************************/
+
+Product.create({
+  name: "guava",
+  price: 10,
+  category: "fruit",
+  tags: ["green", "sweet", "fresh"],
+});
+
+Product.insertMany([
+  {
+    name: "apple",
+    price: 5,
+    category: "fruit",
+    tags: ["red", "sweet"],
+  },
+  {
+    name: "banana",
+    price: 3,
+    category: "fruit",
+    tags: ["yellow", "sweet"],
+  },
+  {
+    name: "broccoli",
+    price: 2,
+    category: "vegetable",
+    tags: ["green", "healthy"],
+  },
+  {
+    name: "milk",
+    price: 4,
+    category: "dairy",
+    tags: ["white", "healthy"],
+  },
+]);
+
+Product.find(); // Get documents in  'product' colelction
+
+Product.find({ name: "guava" }); // Get documents where name = 'guava'
+
+Product.find({ price: { $gt: 5, $lt: 10 } }); // Get documents where 5 < price < 10
+
+Product.find({ name: "banana" }).select({ name: 1, price: 1 }); // Get documents where name = 'banana' and only return name and price
+
+Product.countDocuments({ category: "vegetables" }); // Get count of documents where category = 'vegetables'
+
+Product.updateOne({ name: "guava" }, { price: 15 }); // Update the price of the document where name = 'guava' to 15
+
+Product.deleteOne({ name: "guava" }); // Delete the document where name = 'guava'
+
+Product.deleteMany({ category: "fruit" }); // Delete all documents where category = 'fruit'
+
+/* *****************************************************************
+ * Aggregation
+ * The aggregation pipeline refers to a specific flow of operations that processes, transforms, and returns results.
+ * In a pipeline, successive operations are informed by the previous result.
+ * Check out the MongoDB documentation at: https://www.mongodb.com/docs/manual/aggregation/
+ * ****************************************************************/
+
+// * $match
+// The following aggration pipeline returns all products where price > 80 AND price < 120.
+let pipeline = [
+  {
+    $match: {
+      price: {
+        $gt: 80,
+        $lt: 120,
+      },
+    },
+  },
+];
+
+// or you can use:
+pipeline = [
+  {
+    $match: {
+      price: {
+        $and: [{ $gt: 80 }, { $lt: 120 }],
+      },
+    },
+  },
+];
+
+// Similarly, you can use $or:
+pipeline = [
+  {
+    $match: {
+      category: {
+        $or: [{ $eq: "fruit" }, { $eq: "vegetable" }],
+      },
+    },
+  },
+];
+
+// * $group
+// The following aggregation pipeline returns the total number of products created less than a year ago, in each category.
+pipeline = [
+  {
+    $match: {
+      date: {
+        $gte: new Date(new Date().setFullYear(new Date().getFullYear() - 1)),
+      },
+    },
+  },
+  {
+    $group: {
+      _id: "$category",
+      count: { $sum: 1 },
+    },
+  },
+];
+
+// * $sort
+// The following aggregation pipeline returns top 10 most expensive products.
+// Note: The $sort stage must come before $limit.
+pipeline = [
+  {
+    $sort: {
+      price: -1,
+    },
+  },
+  {
+    $limit: 10,
+  },
+];
+
+// * $project
+// To get the name and price of all products along with their ObjectId:
+pipeline = [
+  {
+    $project: {
+      name: 1,
+      price: 1,
+    },
+  },
+];
+
+// or you can exclude all other fields:
+pipeline = [
+  {
+    $project: {
+      category: 0, // 0 means exclude
+      tags: 0,
+      date: 0,
+    },
+  },
+];
+// Note: You may not use both 0 and 1 in the same projection
+// other than _id, which is included by default:
+pipeline = [
+  {
+    $project: {
+      _id: 0, // exclude ObjectId as well
+      name: 1,
+      price: 1,
+    },
+  },
+];
+
+// * $unwind
+// The following aggregation returns a new document for 'guava' for each of its tags.
+pipeline = [
+  {
+    $match: {
+      name: "guava",
+    },
+  },
+  {
+    $unwind: {
+      path: "$tags", // Name of array field that we want to unwind
+      includeArrayIndex: "arrayIndex", // This will add a new field 'arrayIndex' to each document
+      preserveNullAndEmptyArrays: true, // This will return a document for each tag, even if the 'tags' is null or empty
+    },
+  },
+];