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32 lines
1.2 KiB
Markdown
32 lines
1.2 KiB
Markdown
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# Overview
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Following reading describes implementation details of query execution process. It may clarify some
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internals of GraphQL runtime but is not required to use it.
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# Parsing
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TODOC
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# Validating
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TODOC
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# Executing
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TODOC
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# Errors explained
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There are 3 types of errors in GraphQL:
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- **Syntax**: query has invalid syntax and could not be parsed;
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- **Validation**: query is incompatible with type system (e.g. unknown field is requested);
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- **Execution**: occurs when some field resolver throws (or returns unexpected value).
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Obviously when **Syntax** or **Validation** error is detected - process is interrupted and query is not
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executed.
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GraphQL is forgiving to **Execution** errors which occur in resolvers of nullable fields.
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If such field throws or returns unexpected value the value of the field in response will be simply
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replaced with `null` and error entry will be registered.
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If exception is thrown in non-null field - error bubbles up to first nullable field. This nullable field is
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replaced with `null` and error entry is added to response. If all fields up to the root are non-null -
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**data** entry will be removed from response and only **errors** key will be presented.
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