Understanding the Error
- The error "Not a valid SSG path" in Next.js typically arises when certain routes do not conform to the criteria for Static Site Generation (SSG) as defined in the Next.js framework.
- Static Site Generation in Next.js relies on having clearly defined, valid paths for each page at build time. When these paths are not valid, the error is thrown.
Common Causes of the Error
- Dynamic Routes Without getStaticPaths: If you define a dynamic route but fail to provide all the necessary paths using the
getStaticPaths method, Next.js won't know which pages to generate at build time, leading to this error.
- Invalid or Undefined Paths: When paths returned in
getStaticPaths are invalid, undefined, or improperly formatted, Next.js cannot process these routes correctly.
- Data Fetching Issues: If the data fetching logic within
getStaticPaths does not resolve to a valid list of paths (perhaps due to API errors, incorrect data handling, or empty data sets), this can cause the error as Next.js tries to build pages with incomplete data.
- Mismatched Route Parameters: A common mistake is having inconsistent or mismatched parameters between the defined dynamic route and the returned paths. If these don't align, Next.js won't be able to resolve the paths correctly.
- Incorrectly Using getServerSideProps: Attempting to use
getServerSideProps with the expectation of SSG may lead to confusion and errors since they serve different build processes, with SSG not supporting server-side logic.
- Improper Handling of Catch-All Routes: When using catch-all routes (e.g.,
[...slug].js), if the implementation doesn't account for all variations, certain paths might become invalid for SSG.
Code Example of the Issue
// Incorrect getStaticPaths for a dynamic route
export async function getStaticPaths() {
return {
paths: [
{ params: { id: undefined }}, // Invalid path
{ params: { id: '123' }} // Valid path
],
fallback: 'blocking', // This can only help if paths are correctly defined
};
}
// Correct route definition should return valid paths
export async function getStaticPaths() {
const paths = await fetchPathsFromAPI(); // Hypothetical API call
return {
paths: paths.map((path) => ({
params: { id: path.id.toString() }, // Ensure path is correctly structured
})),
fallback: false,
};
}
