github.com/maeglindeveloper/gqlgen@v0.13.1-0.20210413081235-57808b12a0a0/docs/content/reference/errors.md (about)

     1  ---
     2  linkTitle: Handling Errors
     3  title: Sending custom error data in the graphql response
     4  description: Customising graphql error types to send custom error data back to the client using gqlgen.
     5  menu: { main: { parent: 'reference', weight: 10 } }
     6  ---
     7  
     8  ## Returning errors
     9  
    10  All resolvers simply return an error to be sent to the user. The assumption is that any error message returned
    11  here is appropriate for end users. If certain messages aren't safe, customise the error presenter.
    12  
    13  ### Multiple errors
    14  
    15  To return multiple errors you can call the `graphql.Error` functions like so:
    16  
    17  ```go
    18  package foo
    19  
    20  import (
    21  	"context"
    22  
    23  	"github.com/vektah/gqlparser/v2/gqlerror"
    24  	"github.com/99designs/gqlgen/graphql"
    25  )
    26  
    27  func (r Query) DoThings(ctx context.Context) (bool, error) {
    28  	// Print a formatted string
    29  	graphql.AddErrorf(ctx, "Error %d", 1)
    30  
    31  	// Pass an existing error out
    32  	graphql.AddError(ctx, gqlerror.Errorf("zzzzzt"))
    33  
    34  	// Or fully customize the error
    35  	graphql.AddError(ctx, &gqlerror.Error{
    36  		Path:       graphql.GetPath(ctx),
    37  		Message:    "A descriptive error message",
    38  		Extensions: map[string]interface{}{
    39  			"code": "10-4",
    40  		},
    41  	})
    42  
    43  	// And you can still return an error if you need
    44  	return false, gqlerror.Errorf("BOOM! Headshot")
    45  }
    46  ```
    47  
    48  They will be returned in the same order in the response, eg:
    49  ```json
    50  {
    51    "data": {
    52      "todo": null
    53    },
    54    "errors": [
    55      { "message": "Error 1", "path": [ "todo" ] },
    56      { "message": "zzzzzt", "path": [ "todo" ] },
    57      { "message": "A descriptive error message", "path": [ "todo" ], "extensions": { "code": "10-4" } },
    58      { "message": "BOOM! Headshot", "path": [ "todo" ] }
    59    ]
    60  }
    61  ```
    62  
    63  ## Hooks
    64  
    65  ### The error presenter
    66  
    67  All `errors` returned by resolvers, or from validation, pass through a hook before being displayed to the user.
    68  This hook gives you the ability to customise errors however makes sense in your app.
    69  
    70  The default error presenter will capture the resolver path and use the Error() message in the response.
    71  
    72  You change this when creating the server:
    73  ```go
    74  package bar
    75  
    76  import (
    77  	"context"
    78  	"errors"
    79  
    80  	"github.com/vektah/gqlparser/v2/gqlerror"
    81  	"github.com/99designs/gqlgen/graphql"
    82  	"github.com/99designs/gqlgen/graphql/handler"
    83  )
    84  
    85  func main() {
    86  	server := handler.NewDefaultServer(MakeExecutableSchema(resolvers))
    87  	server.SetErrorPresenter(func(ctx context.Context, e error) *gqlerror.Error {
    88  		err := graphql.DefaultErrorPresenter(ctx, e)
    89  
    90  		var myErr *MyError
    91  		if errors.As(e, &myErr) {
    92  			err.Message = "Eeek!"
    93  		}
    94  
    95  		return err
    96  	})
    97  }
    98  
    99  ```
   100  
   101  This function will be called with the same resolver context that generated it, so you can extract the
   102  current resolver path and whatever other state you might want to notify the client about.
   103  
   104  
   105  ### The panic handler
   106  
   107  There is also a panic handler, called whenever a panic happens to gracefully return a message to the user before
   108  stopping parsing. This is a good spot to notify your bug tracker and send a custom message to the user. Any errors
   109  returned from here will also go through the error presenter.
   110  
   111  You change this when creating the server:
   112  ```go
   113  server := handler.NewDefaultServer(MakeExecutableSchema(resolvers)
   114  server.SetRecoverFunc(func(ctx context.Context, err interface{}) error {
   115      // notify bug tracker...
   116  
   117      return errors.New("Internal server error!")
   118  })
   119  ```
   120