# Populating with the Query Engine API

> Source: https://docs.strapi.io/cms/api/query-engine/populating

The Query Engine API's `populate` parameter loads related data in queries, supporting basic population, selective attributes, filtering nested relations, and polymorphic structures via populate fragments.

:::caution
In most cases you should not use the Query Engine API and rather use the [Document Service API](/cms/api/document-service).

Only use the Query Engine API if you exactly know what you are doing, for instance if you want to use a lower-level API that directly interacts with unique rows of the database.

Please keep in mind that the Query Engine API is not aware of the most advanced Strapi 5 features like Draft & Publish, Internationalization, Content History, and possibly more.
This also means that the Query Engine API will not be able to use `documentId` and will use `id`, which means it could lead to unattended consequences at the database level or partial or incomplete compatibility with Strapi 5 features. 
:::

:::prerequisites
Before diving deeper into the Query Engine API documentation, it is recommended that you read the following introductions:
- the [backend customization introduction](/cms/backend-customization),
- and the [Content APIs introduction](/cms/api/content-api).
:::

Relations and components have a unified API for populating them.

To populate all the root level relations, use `populate: true`:

```js
strapi.db.query('api::article.article').findMany({
  populate: true,
});
```

Select which data to populate by passing an array of attribute names:

```js
strapi.db.query('api::article.article').findMany({
  populate: ['componentA', 'relationA'],
});
```

An object can be passed for more advanced usage:

```js
strapi.db.query('api::article.article').findMany({
  populate: {
    componentB: true,
    dynamiczoneA: true,
    relation: someLogic || true,
  },
});
```

Complex populating can also be achieved by applying `where` filters and select or populate nested relations:

```js
strapi.db.query('api::article.article').findMany({
  populate: {
    relationA: {
      where: {
        name: {
          $contains: 'Strapi',
        },
      },
    },

    repeatableComponent: {
      select: ['someAttributeName'],
      orderBy: ['someAttributeName'],
      populate: {
        componentRelationA: true,
      },
    },

    dynamiczoneA: true,
  },
});
```

When dealing with polymorphic content structures (dynamic zones, polymorphic relations, etc...), it is possible to use populate fragments to have a better granularity on the populate strategy.

```js
strapi.db.query('api::article.article').findMany('api::article.article', {
  populate: {
    dynamicZone: {
      on: {
        'components.foo': {
          select: ['title'],
          where: { title: { $contains: 'strapi' } },
        },
        'components.bar': {
          select: ['name'],
        },
      },
    },

    morphAuthor: {
      on: {
        'plugin::users-permissions.user': {
          select: ['username'],
        },
        'api::author.author': {
          select: ['name'],
        },
      },
    },
  },
});
```