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269 lines
6.6 KiB
ReStructuredText
269 lines
6.6 KiB
ReStructuredText
.. meta::
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:description: Create relationships in Hasura
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:keywords: hasura, docs, schema, relationship, create
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.. _create_relationships:
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Creating relationships
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======================
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.. contents:: Table of contents
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:backlinks: none
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:depth: 2
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:local:
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A relationship from one table/view to another can be created by defining a link between a column of the table/view to a
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column of the other table/view.
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Typically, relationships are defined using foreign-key constraints. But in some cases, it might not be possible to
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use foreign-key constraints to create the relation. For example, while trying to create a relationship involving a view
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as foreign-keys can't be created on views.
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.. _relationships-using-fkey:
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Using foreign keys
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------------------
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Say we created two tables, ``author(id, name)`` and ``article(id, title, content, rating, author_id)``.
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Let us now connect these tables to enable nested queries using a foreign-key:
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Step 1: Add foreign-key constraint
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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In the console, navigate to the ``Modify`` tab of the ``article`` table. Click the ``Add`` button in
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the Foreign Keys section and configure the ``author_id`` column as a foreign-key for the ``id`` column in
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the ``author`` table:
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.. thumbnail:: ../../../../img/graphql/manual/schema/add-foreign-key.png
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:alt: Add foreign-key constraint
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Step 2: Create an object relationship
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Each article has one author. This is an ``object relationship``.
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The console infers this using the foreign-key created above and recommends the potential relationship in the
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``Relationships`` tab of the ``article`` table.
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Add an ``object relationship`` named ``author`` for the ``article`` table as shown here:
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.. thumbnail:: ../../../../img/graphql/manual/schema/add-1-1-relationship.png
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:alt: Create an object relationship
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We can now run a nested object query that is based on this ``object relationship``.
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Fetch a list of articles and each article's author:
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.. graphiql::
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:view_only:
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:query:
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query {
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article {
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id
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title
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author {
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id
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name
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}
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}
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}
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:response:
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{
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"data": {
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"article": [
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{
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"id": 1,
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"title": "sit amet",
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"author": {
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"name": "Anjela",
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"id": 4
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}
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},
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{
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"id": 2,
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"title": "a nibh",
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"author": {
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"name": "Beltran",
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"id": 2
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}
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},
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{
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"id": 3,
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"title": "amet justo morbi",
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"author": {
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"name": "Anjela",
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"id": 4
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}
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}
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]
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}
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}
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Step 3: Create an array relationship
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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An author can write multiple articles. This is an ``array relationship``.
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You can add an ``array relationship`` in the same fashion as an ``object relationship`` as shown above.
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Add an ``array relationship`` named ``articles`` for the ``author`` table as shown here:
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.. thumbnail:: ../../../../img/graphql/manual/schema/add-1-many-relationship.png
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:alt: Create an array relationship
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We can now run a nested object query that is based on this ``array relationship``.
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Fetch a list of authors and a nested list of each author's articles:
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.. graphiql::
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:view_only:
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:query:
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query {
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author {
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id
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name
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articles {
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id
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title
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}
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}
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}
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:response:
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{
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"data": {
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"author": [
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{
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"id": 1,
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"name": "Justin",
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"articles": [
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{
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"id": 15,
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"title": "vel dapibus at"
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},
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{
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"id": 16,
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"title": "sem duis aliquam"
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}
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]
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},
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{
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"id": 2,
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"name": "Beltran",
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"articles": [
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{
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"id": 2,
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"title": "a nibh"
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},
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{
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"id": 9,
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"title": "sit amet"
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}
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]
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},
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{
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"id": 3,
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"name": "Sidney",
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"articles": [
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{
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"id": 6,
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"title": "sapien ut"
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},
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{
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"id": 11,
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"title": "turpis eget"
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},
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{
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"id": 14,
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"title": "congue etiam justo"
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}
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]
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}
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]
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}
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}
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.. _create_manual_relationships:
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Using manual relationships
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--------------------------
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Let's say you have a table ``author (id, name)`` and a view ``author_avg_rating (id, avg)`` which has the
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average rating of articles for each author.
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Let us now create an ``object relationship`` called ``avg_rating`` from the ``author`` table to the
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``author_avg_rating`` view using a manual relationship:
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Step 1: Open the manual relationship section
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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- Open the console and navigate to the ``Data -> author -> Relationships`` tab.
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- Click on the ``Configure`` button:
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.. thumbnail:: ../../../../img/graphql/manual/schema/manual-relationship-btn.png
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:alt: Open the manual relationship section
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Step 2: Define the relationship
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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The above step will open up a section as shown below:
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.. thumbnail:: ../../../../img/graphql/manual/schema/manual-relationship-create.png
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:alt: Define the relationship
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In this case:
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- **Relationship Type** will be: ``Object Relationship``
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- **Relationship Name** can be: ``avg_rating``
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- **Reference** will be: ``id -> author_avg_rating . id`` *(similar to defining a foreign-key)*
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Step 3: Create the relationship
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Now click on the ``Save`` button to create the relationship.
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We can now run a nested object query that is based on this ``object relationship``.
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Fetch a list of authors with the average rating of their articles:
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.. graphiql::
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:view_only:
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:query:
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query {
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author {
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id
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name
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avg_rating {
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avg
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}
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}
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}
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:response:
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{
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"data": {
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"author": [
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{
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"id": 1,
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"name": "Justin",
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"avg_rating": {
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"avg": 2.5
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}
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},
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{
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"id": 2,
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"name": "Beltran",
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"avg_rating": {
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"avg": 3
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}
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},
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{
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"id": 3,
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"name": "Sidney",
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"avg_rating": {
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"avg": 2.6666666666666665
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}
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}
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]
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}
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}
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