So, I have a database with the following collections. 

(Using Integers to represent the object IDs)

**Books:**

```
books = [
  { _id: 1, title: "Harry Potter" },
  { _id: 2, title: "The maze runner" }
  ...
]

```

**Customers:** 

```
customers = [
  { _id: 1, name: "John" },
  { _id: 2, title: "Jane"}
  ...
]

```

**Recommendations:** 

```
recommendations = [
  {
    customerID: 1,
    recommendations: [
      { bookID: 1, likelihood: 0.9 },
      { bookID: 2, likelihood: 0.8 }
    ]
  },
  {
    customerID: 2,
    recommendations: [
      { bookID: 2, likelihood: 0.9 },
      { bookID: 1, likelihood: 0.8 }
    ]
  }
  ...
]

```

Now when a request is sent to my server, containing `customerID` in the `req.body`, i want to return the recommended books for that customer, with the likelihood appended to them.

**i.e :**

```
desiredResult = [
  {
    _id: 1,
    title: "Harry Potter",
    likelihood: 0.9
  },
  {
    _id: 2,
    title: "The maze Potter",
    likelihood: 0.8
  }
  ...
]

```

Please, what is the MongoDB aggregation query to achieve this ?