Dgraph: How do you query for strings that start with a specific sequence of letters? - dgraph

Question

For example, let's say your database contains a bunch of People{ name } objects, and you want to find everyone whose name starts with the letter "H" or "Mi".

Answer 1

You should use Regex https://docs.dgraph.io/query-language/#regular-expressions
But, regex accepts at least 3 characters.
Other way you could do is using "has" function and ordering by the predicate.
https://docs.dgraph.io/query-language/#has
{
me(func: has(name), first: 50, orderasc: name) {
name
}
}
But with 'Has' function you don't have full control. It will follow an alphabetical order.
One way to have this level of control is to create a pseudo-indexing structure. Every time you add a user you relate him to a tree that will play the role of indexing. And through this tree you can count and traverse the edge.
e.g:
Let's assume you know the UID of your tree (or that you use Upser Block).
_:NewUser <name> "Lucas" .
_:NewUser <pred1> "some1" .
_:NewUser <pred2> "some2" .
# Now we gonna relate Lucas to our tree and <0x33f> is the uid for the letter L of "Lucas"
<0x33f> <firstCharacter> _:NewUser . #This is a reverse record (you don't need to use #reverse tho)
The same example using Upsert Block:
upsert {
query {
v as var(func: type(myTree)) #filter(eq(letter, "L"))
}
mutation {
set {
_:NewUser <name> "Lucas" .
_:NewUser <pred1> "some1" .
_:NewUser <pred2> "some2" .
uid(v) <firstCharacter> _:NewUser .
}
}
}
A basic search in the tree would be like:
{
q(func: type(myTree)) #filter(eq(letter, "L")) {
letter
firstCharacter { name pred1 pred2 }
}
}
Or
{
q(func: type(myTree)) #filter(eq(letter, "L")) {
letter
count(firstCharacter)
}
}
Cheers.