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36 lines
1.3 KiB
Markdown
36 lines
1.3 KiB
Markdown
# 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 - the process is interrupted and
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the query is not executed.
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Execution process never throws exceptions. Instead, all errors are caught and collected in
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execution result.
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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 an exception is thrown in the non-null field - error bubbles up to the first nullable field.
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This nullable field is replaced with **null** and error entry is added to the result.
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If all fields up to the root are non-null - **data** entry will be removed from the result
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and only **errors** key will be presented.
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