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DGraph Cheatsheet

DGraph Cheat sheet

How it works?

Dgraph is a graph databases. It stores data in a similar fashion for any type of collections. To differentiate the collection list, we may add a predicate, let's say "_type" indicate the type of collection / table. Example: User will have _type='users' and Role will have _type='roles'. ID field in dgraph is named "uid"

Ports

Client may connect to server nodes on port 9080 for grpc connection. Server nodes uses grpc 7080 to talk to zero node. You may call http admin rest call to server node on port 8080.

https://docs.dgraph.io/deploy#ports-used-by-different-nodes

Standard query (graphql alike)

query an object by id. with_role returns roles. "roles" indicate in the below code is a alias name to "with_role"

{
  user(func: uid(0xc351)) {
    first_name
    last_name
    email

    roles: with_role {
    	uid
    	name
    }
  }
}

To know how relation works for "with_role", refer here

To sort the list of objects, the predicate/field need to be indexed. The index type will depend on the filter / sorting and predicate type. You may add multiple index to a predicate.

  • string - @index(fulltext / exact / term)
  • int / float- @index(int) / @index(float)
  • dateTime @index(day/hour)

example:

first_name: string @index(term) @index(fulltext) .

Refer here for index docs

To query list, example below shows 2 different type of query.

  • roles - list all roles, with user that has relation with_role with respective role
  • users - with pagination limit of 10, offset 0 (since not indicated), ordered by created_at desc with field set "with_role"
  • roles_count - count all roles
query all($id: string){
	roles(func: eq(_type, "roles"))  {
		uid
		name
		created_at
		updated_at
    
    users: ~with_role {
      uid
      email
    }
	}
  
  users(func: eq(_type, "users"), first: 10, orderdesc: created_at) @filter(has(with_role))   {
		uid
		email
		first_name
		last_name
		ip_address
		created_at
		updated_at
		roles : with_role {
			uid
			name 
		}
		company : work_for {
			uid
			code
			name
			status
			country
			created_at
			updated_at 
			 
		}
	}
	
	roles_count(func: eq(_type, "roles"))  {
		count(uid)
	}
}

for more queries references:

Queries

mutation (update and delete)

update / create object using json aka. mutation

{
  "set": [
    { "first_name": "ahmad", "last_name": "bin osman", "email": "test@example.com" }
  ]
}

update using RDF mutation

  • <0x01> - uid
  • - predicate / field
  • "Alice" - value for the field
  • @ru | @fr - suffix for respective language
mutation {
  set {
    <0x01> <name> "Alice" .
    <0x01> <name> "Алисия"@ru .
    <0x01> <name> "Adélaïde"@fr .
  }
}

for more mutations:

to delete a single field

mutation {
  delete {
     <0x01> <first_name> * .
  }
}

you may also specify specify value to delete.

Example below delete the role by uid <0x02> relation from user 0x01.

Role 0x02 will remain in database

mutation {
  delete {
     <0x01> <with_role> <0x02> .
  }
}

to delete entire object / record (not tested)

mutation {
  delete {
    <0x01> * * .
  }
}

to delete everything (not tested)

mutation {
  delete {
    * * * .
  }
}

Relations

To declare a relation between two object, for example user with roles, 0x01 is the user uid, and 0x02 is the role uid.


mutation {
  set {
    <0x01> <with_role> <0x02> .
  }
}

Ensure that you have set the schema for the predicate like below:

with_role: uid @reverse .

@reverse is indicate how roles can query users from the opposite direction. with @reverse declared, you may now query users from role

{
  role(func: uid(0x02)) {
    uid
    name

    users: ~with_role {
    	uid
    	first_name
    	last_name
    	email
    }
  }
}

Please note that if you attempt to mutate delete one or more relation,then query for only the relation field, please add also uid predicate of the main object. This is to avoid no record found error in DGO library. Example:

Don't do this:

{
  user(func: uid(0x01)) {
    roles: with_role {
      uid
      name
    }
  }
}

Do this:

{
  user(func: uid(0x01)) {
    uid
    roles: with_role {
      uid
      name
    }
  }
}

For other schema queries

(https://docs.dgraph.io/v0.7.4/query-language/#fetching-schema)

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