Pagination

Using pagination and slicing to work with search queries

Use Pagination to query a list of data in discrete parts. Also, use the cursor-based pagination to select which set of results to retrieve from a connection.

Implementing pagination in data-heavy queries helps to:

  • Optimize the application performance

  • Reduce the load time the application is rendering the results in the UI.

Use Slicing to fetch exactly the number of results from the data.

Learn more about Cursors here: https://relay.dev/graphql/connections.htm

Pagination

Within pagination, connections retrieve a list of nodes. A node is an object that has a global ID. Nodes are said to be connected by edges.

  • node: Used to select the fields that you want to retrieve from the node at each edge.

  • edges: Used to select the fields that you want to retrieve from each edge in the connection. The edges field is similar to a for-loop because it retrieves the selected fields from each edge in the connection.

query {
 edges 
  {
    node
     {
      name
     }
  }
}

The following example retrieves the list of restaurants:

{
  restaurantSearch(
    query:"Mexican Restaurant") 
  {
    edges
    {
     node
      {
        name
       }   
    }
 }
}

Cursor-based Pagination

A cursor is a unique string that identifies a particular row. You can include the following fields in your queries to paginate your results:

  • pageInfo:Each connection can return a PageInfo object which contains general information about the particular page returned. This object includes:

    • hasNextPage: displays whether there are results in the connection after the current segment.

    • hasPreviousPage displays whether there are results in the connection before the current segment.

    • startCursor and endCursor: return non-null opaque strings. Both must be the cursors corresponding to the first and last nodes in edges, respectively.

    • endCursor

  • cursor: A marker for an edge's position in the connection.

Forward pagination arguments

To enable forward pagination arguments, use the following fields:

  • first:it takes a non-negative integer.

  • after: It takes the cursor type and retrieves results after that position.

Pass the cursor of the last edge on the previous page for after.

Backward pagination arguments

  • last:it takes a non-negative integer.

  • before: It takes the cursor type and retrieves the results before that position.

Pass the cursor of the first edge on the next page for before.

Examples

Fetching results using Cursor based pagination

In the following example, use pageInfo and cursor fields in the queries to paginate the results.

{
  restaurantSearch(
    query:"Mexican Restaurant"
    distance: 100
    meals: "meat"
    isOpen:true
    first:3
) 
  {
edges
    {
      node{
        name
        cityTown
        country
        recommendation
      }  
       cursor
    }
    pageInfo{
      hasNextPage
      hasPreviousPage
      startCursor
      endCursor
    }
}
}

The result retrieves three results from the beginning of the connection, and they include a cursor for each edge. In addition, we asked for hasNextPage; that will tell us if there are more edges available, or if we’ve reached the end of this connection.

Fetching results using after parameter

In the following example, use after argument to pass the information of a specific cursor, so results display the information after that cursor. For instance, define the after parameter with the YXJyYXljb25uZWN0aW9uOjI= value, which corresponds to the "name": "Tom's Restaurant" last result retrieved in the previous example:

{
  restaurantSearch(
    query:"Mexican Restaurant"
    distance: 100
    meals: "meat"
    isOpen:true
    first:3
    after: "YXJyYXljb25uZWN0aW9uOjI="
) 
  {
edges
    {
      node{
        name
        cityTown
        country
        recommendation
      }  
       cursor
    }
    pageInfo{
      hasNextPage
      hasPreviousPage
      startCursor
   
    }
}
}

The results retrieve the next three restaurants listed immediately after the "Tom's Restaurant" which has been retrieved in a previous example.

{
  recipeSearch(
    meals: ["Breakfast"],
    query: "coconut",
    first: 3,
    after: "YXJyYXljb25uZWN0aW9uOjEw"
  ) {
    edges {
      node {
        id
        name
      }
      cursor
    }
    pageInfo {
      endCursor
      hasNextPage
    }
  }
}

We can continue the pagination using the endCursor 

{
  restaurantSearch(
    query:"Mexican Restaurant"
    distance: 100
    meals: "meat"
    isOpen:true
    first:3
    after: "YXJyYXljb25uZWN0aW9uOjI="
) 
  {
edges
    {
      node{
        name
        cityTown
        country
        recommendation
      }  
       cursor
    }
    pageInfo{
      hasNextPage
      hasPreviousPage
      startCursor
      endCursor
    }
}
}

Fetching results using first parameter

The following example uses the first and after aruments to modify the edges returned by the connection, returning edges after the after cursor, and returning the 3 first edges.

{
  restaurantSearch(
    query:"Mexican Restaurant"
    first:3
    after: "YXJyYXljb25uZWN0aW9uOjI="
) 
  {
edges
    {
      node{
        name
        cityTown
        country
      }  
       cursor
    }
    pageInfo{
      hasNextPage
      hasPreviousPage
    }
}
}

Slicing

In the following example, we retrieve the first 10 results from a recipe search containing the meal_tag Breakfast and including the term coconut.

{
  restaurantSearch(
    query:"Mexican Restaurant"
    meals: "meat"
    isOpen:true
    first:10
) 
  {
edges
    {
      node{
        name
        cityTown
        country
        recommendation
      }  
    }
}
}

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