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graphql-php/docs/how-it-works.md
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Overview

Following reading describes implementation details of query execution process. It may clarify some internals of GraphQL runtime but is not required to use it.

Parsing

TODOC

Validating

TODOC

Executing

TODOC

Errors explained

There are 3 types of errors in GraphQL:

  • Syntax: query has invalid syntax and could not be parsed;
  • Validation: query is incompatible with type system (e.g. unknown field is requested);
  • Execution: occurs when some field resolver throws (or returns unexpected value).

Obviously when Syntax or Validation error is detected - process is interrupted and query is not executed.

GraphQL is forgiving to Execution errors which occur in resolvers of nullable fields. If such field throws or returns unexpected value the value of the field in response will be simply replaced with null and error entry will be registered.

If exception is thrown in non-null field - error bubbles up to first nullable field. This nullable field is
replaced with null and error entry is added to response. If all fields up to the root are non-null - data entry will be removed from response and only errors key will be presented.