---
title: Collections
slug: v4-7/document-model/collections
docTags: 
createdAt: 2023-08-13T16:32:45.845Z
---

Ditto syncs and queries documents through a combination of collection names and document identifiers (`_id`). A collection is a grouping of documents, like *tables* in a relational database system but far simpler and more flexible.

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# Structuring Collections

While it is good practice for documents within a collection to share a similar structure — for instance, all car-related documents stored in the `cars` collection contain fields `'make'`, `'model'`, and `'year'`  — structural uniformity is not mandatory. 

There is no limit to the number of collections you can have in your data model, so create as many collections as you need. 

For more information, see [Bad Pattern: Large Documents](docId\:B4Bj0z0xxoHo2KD13tYSL).

# Managing Collections

Every document must be associated with a collection, even if only one document exists within that collection.

There are no explicit steps to managing collections; Ditto implicitly creates collections, assigns documents, and organizes references based on the documents being stored.

# Querying Collections

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When querying, database interactions occur with collections rather than individual documents.

For instance, the query on the right searches the entire `cars` collection once executed.
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DQL

```sql
SELECT * FROM cars
```
:::
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## Declaring Types

To declare types, prefix the collection name with the `COLLECTION` keyword followed by a *type definition*. A type definition expresses the data types for the fields. 

For example, here querying is against the `cars` collection with a field `properties` of data type `MAP`:

:::CodeblockTabs
DQL

```sql
SELECT * FROM COLLECTION cars (properties MAP)
```
:::

For complete DQL syntax, see *Ditto Query Language *> [Types and Definitions](docId\:so0GVjLPrqJbUaBmG39xA).