Python - parse graphql, add something, then back to the query string

Question

I'm trying to use python to parse a graphql query, alter it, and turn it back into a string query that I can pass to the graphql server.

Specifically, I'm trying to ensure that a query will always have the pageInfo paging information, so if I'm executing a query, I will always be able to automatically page through the results, even if a user might forget that stanza in their actual query.

It seems surprisingly difficult to parse a graphql query into something useful, and then be able to go from the parsed data representation back to the query string. Is there a library that google isn't able to turn up for me?

Thanks so much for any help!

Daniel Rearden · Accepted Answer · 2020-06-09 18:55:49Z

3

The core library includes a parse function for parsing strings into AST and a print_ast function for converting the AST back to a string.

answered Jun 9, 2020 at 18:55

Daniel Rearden

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1 Comment

Hoopes Over a year ago

Hi Daniel, thanks! I somehow overlooked print_ast - you don't happen to have any examples of how to edit this ast, do you? Much obliged!

Presto · Accepted Answer · 2023-06-16 13:29:17Z

1

I've just faced a similar problem. For future reference: the way you edit the AST is by creating a visitor class that will enter the tree and modify it to your liking. It's described in the documentation here. For example, in order to remove field named attributes I used following code:

from graphql import parse, print_ast
from graphql.language.visitor import visit, Visitor, REMOVE, IDLE

class RemoveAttributesVisitor(Visitor):
    def enter_field(self, node, key, parent, path, ancestors):
        if node.name.value == "attributes":
            return REMOVE
        return IDLE

ast = parse(PRODUCT_QUERY)
new_ast = visit(ast, RemoveAttributesVisitor())
updated_query = print_ast(new_ast)

answered Jun 16, 2023 at 13:29

Presto

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