### File

`src/lib/sub-collection-writer.ts`

### Description

The ability to place docs and collection n deep but also flatten the it in order to reduce reads. It becomes a balance between speed and economy. Since multiple docs can be read simultaneously but will cost more. These classes aim to make it easy to control that.

Allows you to have a complex deep object and write it to firestore by splitting it up in to collections and documents.

Example services object that we wish to save to firestore.

    const services = {
       name: 'example services',
       address: {
          zipcode: 12345,
          city: 'example city',
          line1: '12 example rd'
       },
       dishes: [
         {
           name: 'dish1',
           images: [
             {url: example.jpg},
             {url: example2.jpg}
           ]
         },
         {
           name: 'dish2',
           images: [
             {url: example.jpg},
             {url: example2.jpg}
           ]
         }
       ]
       reviews: [
         {
            score: 5
            text: 'decent food'
         },
         {
            score: 8
            text: 'good food'
         },
       ]
    }

You would be able to save this data 'as is' to a single firestore document using arrays and maps. The problem comes when you later on wish to add/delete or alter an image of dish.

Another issue is that you might have thousands of reviews and since they are all saved in the same document. If for example you wish to show a list of all restaurants and all you want to show is the name before a user clicks the services you would still have to download the entire services object containing all those thousands of reviews. This would be ok in terms of cost of reads but very expensive in terms of performance. Each services object would be huge, killing the user's data plan and slowing down your site.

It would be much better to make reviews a collection inside services. That way you could show the services name without downloading all the reviews. If you wish to show an average review score the most efficient way would be to to calculate that each time you update the review collection and adding the average to the services document.

What this wrapper intends to do is to simplify saving some data in sub collections without changing the way you work with the data. So you could have a services object that contains all the data and when you add it to firestore the data is automatically placed in your sub collections without you having to worry about it after you initially set it up.

Another huge advantage to separating your data in to sub collections is that it allows you to choose between performance and cost. Saving the data to one large document would save your firestore read/writes and could potentially make a big difference in terms of cost depending on your application. But it would also slow it down as explained above. Splitting your data up in to sub collections allows you to asyncronously read/write those collections at the same time.

So if you compare one large document and a small document with 4 subcollections of about equal size. It would require 5 firestore reads instead of 1 if each sub collection contains 1 document. But the speed could also potentially be 5X faster since all those parts are read at the same time.

Using SubCollectionWriters and SubCollectionQueries allows you to create the perfect compromise between ease of working with the firestore database, cost and performance.

- address (collection)
- reviews (collection)
- dishes (collection)
  - images (collection)

### Example

    const subCollectionWriters: SubCollectionWriter[] = [
    { name: 'data' },
    {
    name: 'images',
    docId: 'data',  // images is an array but since a docId is given it be saved in a single doc
    },
    {
    name: 'variants',
    subCollectionWriters: [  // sub collection inside a sub collection
    { name: 'otherData'}
    ]
    }
    ];

### Index

###### Properties
Optional docId Optional isFlat name Optional subCollectionWriters

### Properties

Optional docId
Type : `string`
Defined in src/lib/sub-collection-writer.ts:109
if the data to be written is an array and a docId is given the array is saved as single document under that docId. if not docId is given the array will be saved as individual documents with random names. if no docId is given and the data is an object a single document will be created using a default name i.e this.defaultDocId

Optional isFlat
Type : `boolean`
Default value : `false`
Defined in src/lib/sub-collection-writer.ts:117
if true then the next level subCollectionWriters will be placed at the same level as this with a reference back to the linked data, good for secure subcols

name
Type : `string`
Defined in src/lib/sub-collection-writer.ts:102
the name of the subCollection to be created. If a key in the data to be written is the same as this name it will be saved separately in a sub collection.

Optional subCollectionWriters
Type : `SubCollectionWriter[]`
Defined in src/lib/sub-collection-writer.ts:112
each collection can contain other sub collections

    export class SubCollectionWriter {
      /** the name of the subCollection to be created. If a key in the data to be written is the same as this name it will be
       * saved separately in a sub collection.
       */
      name: string;

      /** if the data to be written is an array and a docId is given the array is saved as single document under that docId.
       *                    if not docId is given the array will be saved as individual documents with random names.
       *                    if no docId is given and the data is an object a single document will be created using a default name
       *                    i.e this.defaultDocId
       */
      docId?: string;

      /** each collection can contain other sub collections */
      subCollectionWriters?: SubCollectionWriter[]; // sub/sub collections

      /** if true then the next level subCollectionWriters will be placed at the same level as this with a reference back
       * to the linked data, good for secure subcols
       */
      isFlat?: boolean = false;
    }

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