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Mongoose Fundamentals

Queries

At this point, we will start creating instances in a MongoDB database, then query the database for the values we saved. All of the method calls and queries will be passed to runWithDatabase().

If we wanted to search for the poem that we saved to the database, we could write a Mongoose query and call .findOne() on our Poem model:

runWithDatabase(async () => {
   Poem.create(poemProperties)

   const poemMatch = await Poem.findOne({ title: 'Rewrite Reality' });

   console.log(`Found poem: ${poemMatch.body}`);
});

.findOne() returns a document that has a title path with the value 'Rewrite Reality'. We confirm this by using console.log() to see the value of the path body for the returned document.

This is good when we are looking for one document. What if we wanted to find all the documents that matched a specified criteria? We can use .find(), which returns an array of all the documents that match the argument passed to it.

Imagine we had a collection of documents with the following values:

const manyPoems = [
  {
    title: "Rewrite Reality" ,
    body: ["Re-imagine the consumption of the stagnant status quo",
               "No matter how nice you dress",
               "The emperor is still wearing no clothes"],
    published: false ,
},
  {
    title: "Phasing",
    body: ["I imagine myself a second moon;",
              "waning in and out of sequence with the tides"],
    published: true,
},
  {
    title: "One of Those Days",
    body: ["My shirt and spirit”,
             "are bent inside-out-backwards"],
    published: true,
}
]

In the example below, we create the above documents using a Poem model, then we use the find method to return all poems with a published property equal to true:

runWithDatabase(async () => {
  Poem.create(manyPoems);

  let publishedPoems = await Poem.find({ published: true })

  // Check that it works by logging the number of returned documents
  console.log(`Published Poems: ${publishedPoems.length}`)
});

To the right, we’ve added items.js to your project. It contains an array of items that we will save to the MongoDB database. In exercise.js, we import the items from items.js and use MagicItem.create() to save the items as documents to our database.

Instructions

Follow the steps below to write a query using .findOne() to locate the document in your database with the item: "cloak".

Inside runWithDatabase() and below .create(), add a let variable named finder and set it equal to await and then your query.

Before running your script in the terminal, add this on the following line:

console.log(`Found one: ${finder.item}`);

Run your database query using the following command in the terminal: node exercise.js.

Add a second query to your code, which uses .find() to locate all magicObject documents that have a unitCost less than 50.

You can use the mongoose query operator $lt. $lt selects the documents where the value of the field is less than (i.e. <) the specified value. The syntax is:

.find({field: {$lt: value} }).

Create a let variable named cheapObjects and set it equal to await and then your query.
Before running your script in the terminal, you can add this line after your code:

console.log(`Found ${cheapObjects.length} magic objects`);

Run your database query using the following command in the terminal: node exercise.js.

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