Ajv: Upon error, does `ajv` also display the line number details ?

[vivekgalatage]

When loading a json file which will be validated against a schema and if there is any validation error, does ajv show the line number (i.e. position of the property in error) from the json string?

[epoberezkin]

Ajv doesn’t work with JSON strings, only with objects. It returns JS or JSON-pointers in errors. You can use json-source-map to map them to locations in JSON strings

[vivekgalatage]

Thank you! The json-source-map works great for my requirement. :-)

[marjan-georgiev]

@vivekgalatage could you point me to an example on how you achieved that please?

[DeepTom]

@vivekgalatage , Do you have any small example to share how you used json-source-map for custom errors.

[MattiSG]

In order to save others the hour it took me to get it right:

const ajv = require('ajv');

const validator = new ajv({
  allErrors: true,  // do not bail, optional
  jsonPointers: true,  // totally needed for this
});

function assertValid(schema, subject) {
  const valid = validator.validate(schema, subject);

  if (!valid) {
    let errorMessage = '';
    const sourceMap = jsonSourceMap.stringify(subject, null, 2);
    const jsonLines = sourceMap.json.split('\n');
    validator.errors.forEach(error => {
      errorMessage += '\n\n' + validator.errorsText([ error ]);
      let errorPointer = sourceMap.pointers[error.dataPath];
      errorMessage += '\n> ' + jsonLines.slice(errorPointer.value.line, errorPointer.valueEnd.line).join('\n> ');
    });
    throw new Error(errorMessage);
  }
}