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Creating and removing one-to-one and one-to-many references

Hypi can provide one-to-one or one-to-many references for tables.

Let’s say you want to connect Table A to Table B through one common field ‘C’. So, table A has this field C of type B. This is the one-to-one reference. If field C is an array or list of type B, it is a one-to-many kind of reference.

For creating a reference, Hypi has the built-in function link. The references can be removed using the unlink function.

Let’s check the signatures of link and unlink functions.

link(
    from:HypiMutationType!
    to:HypiMutationType!
    via:String!
    whereFromID:String!
    andToID:String!
):Boolean!
unlink(
    from:HypiMutationType!
    to:HypiMutationType!
    via:String!
    whereFromID:String!
    andToID:String!
):Boolean!
ParameterDescriptionExample
fromThe data type from where reference needs to be createdfrom: ‘Author’
toThe data type to be referredto: ‘Book’
viaThe field of object ‘to’ in the object ‘from’Booklist
whereFromIDHypi ID of the Object of type ‘from’ that needs an entry of object ‘to’‘Author1’
andToIDHypi ID of the Object of type ‘to’ that needs to be entered into the object of type ‘from’‘Book1’

Examples​

To go through examples, we will need below schema.

type Book {
    title: String
    authorid: Int
    price: Float
}

type Author {
    name: String
    age: Int
    bestbook: Book
    booklist: [Book!]
}

Here, the field bestbook will be used to generate one-to-one reference between table Author and table Book. Also, the field booklist will be used to generate one-to-many kind of references.

Let’s add data in the table Author and table Book as follows.


mutation Upsert($values: HypiUpsertInputUnion!) {
  upsert(values: $values) {
    id
  }
}

One-to-One Reference​

If you want to enter Book1 as the bestbook of Author1, you may link Author1 with Book1 via field bestbook.

mutation {
    link(from:Author,to:Book,
    via:"bestbook",whereFromID:"Author1",andToID:"Book1")
}

Linking the tables results in the insertion of data from Book1 into the field Bestbook of Author1. Now, retrieve data of Author using find function and verify.

{
  "data": {
    "find": {
      "edges": [
        {
          "node": {
            "name": "Dan Brown",
            "age": 56,
            //Book1 Inserted
            "bestbook": {
              "title": "Inferno",
              "authorid": 1
            },
            "booklist": [
              {
                "title": "Da Vinci Code",
                "authorid": 1
              },
              {
                "title": "The Last Symbol",
                "authorid": 1
              }
            ]
          },
          "cursor": "Author1"
        }
      ]
    }
  }
}

You may remove the reference using the unlink function.

mutation{
    unlink(from:Author,to:Book,
    via:"bestbook",whereFromID:"Author1",andToID:"Book1")
}

This results in the setting of the value of bestbook as null. Book1 data remains as it is. But the object simply gets removed from the field bestbook of object Author1.

{
  "data": {
    "find": {
      "edges": [
        {
          "node": {
            "name": "Dan Brown",
            "age": 56,
             //Book1 entry removed
            "bestbook": null,
            "booklist": [
              {
                "title": "Da Vinci Code",
                "authorid": 1
              },
              {
                "title": "The Last Symbol",
                "authorid": 1
              }
            ]
          },
          "cursor": "Author1"
        }
      ]
    }
  }
}

One-to-Many Reference:​

The link function works on an array as well. You may link to the booklist field from the Author1 object to Book1. So an entry of Book1 gets added into the booklist array of Author1.

mutation{
    link(from:Author,to:Book,
    via:"booklist",whereFromID:"Author1",andToID:"Book1")
}

You may retrieve data from Author1 using find function.

{
  "data": {
    "find": {
      "edges": [
        {
          "node": {
            "name": "Dan Brown",
            "age": 56,
            "bestbook": null,
            "booklist": [
              {
                "title": "Da Vinci Code",
                "authorid": 1
              },
              {
                "title": "The Last Symbol",
                "authorid": 1
              },
                //Book1 inserted in the array
              {
                "title": "Inferno",
                "authorid": 1
              }
            ]
          },
          "cursor": "Author1"
        }
      ]
    }
  }
}

Unlinking the reference would simply remove the entry Book1 from the booklist. The Book1 object would not get deleted from the platform. But its entry would be removed from the array.

mutation{
    unlink(from:Author,to:Book,
    via:"booklist",whereFromID:"Author1",andToID:"Book1")
}

Retrieve Author1 data to get following result.

{
  "data": {
    "find": {
      "edges": [
        {
          "node": {
            "name": "Dan Brown",
            "age": 56,
            "bestbook": null,
            "booklist": [
              {
                "title": "Da Vinci Code",
                "authorid": 1
              },
              {
                "title": "The Last Symbol",
                "authorid": 1
              }
                //Book1 removed from the array
            ]
          },
          "cursor": "Author1"
        }
      ]
    }
  }
}

Using link and unlink function you may add or remove objects from the array of objects.

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