hasura/graphql-engine · error · Error

cannot merge fields with different arguments on the same ali

Error message

cannot merge fields with different arguments on the same alias: {alias}

What it means

Thrown by the FieldsCanMerge rule when two fields merged under the same response key pass different arguments, e.g. `{ f(field: A), f(field: B) }` or the same aliased field with different argument sets via fragments. Fields that merge into one response entry must either share identical arguments or not take conflicting ones; the error reports the alias and both source positions (Option<spanning::SourcePosition>) so you can jump to both occurrences in the document.

Source

Thrown at v3/crates/graphql/lang-graphql/src/validation/error.rs:67

        field_name: ast::Name,
    },
    #[error(
        "different fields {field1} and {field2} cannot be merged under the same alias: {alias}"
    )]
    FieldsConflictDifferentFields {
        alias: ast::Alias,
        field1: ast::Name,
        field2: ast::Name,
    },
    #[error(
        "fields of different type {type1} and {type2} cannot be merged under the same alias: {alias}"
    )]
    FieldsConflictDifferingTypes {
        alias: ast::Alias,
        type1: ast::Type,
        type2: ast::Type,
    },
    #[error("cannot merge fields with different arguments on the same alias: {alias}")]
    FieldsConflictDifferingArguments {
        alias: ast::Alias,
        location1: Option<spanning::SourcePosition>,
        location2: Option<spanning::SourcePosition>,
    },
    #[error("the string {str} in the provided json value is not a valid GraphQL name")]
    NotAValidName { str: String },
    #[error("expected a value of type {expected_type} but found a value of type {actual_type}")]
    IncorrectFormat {
        expected_type: &'static str,
        actual_type: &'static str,
    },
    #[error("a null value found when expected a value of not nullable type: {expected_type}")]
    UnexpectedNull { expected_type: ast::Type },
    #[error("the field {field_name} on type {type_name} is not found")]
    InputFieldNotFound {
        type_name: ast::TypeName,
        field_name: ast::Name,

View on GitHub (pinned to 724551b9ae)

Solutions

1. Give each variant a distinct alias (`{ first: user(id: 1), second: user(id: 2) }`)
2. Make the arguments identical across all occurrences if a single merged result is intended
3. Check fragments spread into the same selection set for duplicated fields with differing arguments

Example fix

// before
{ user(id: 1) { name } user(id: 2) { name } }
// after
{ u1: user(id: 1) { name } u2: user(id: 2) { name } }

for (key, fields) in group_by_response_key(selection) { for w in fields.windows(2) { assert!(same_args(&w[0].arguments, &w[1].arguments), "alias {key} used with differing arguments"); } }

fn same_args(a: &[(Name, Value)], b: &[(Name, Value)]) -> bool { a == b }

match validate(doc) { Err(Error::FieldsConflictDifferingArguments { alias, .. }) => give_unique_alias(alias), r => r }

When it happens

Trigger: Repeating a field with the same alias but different argument values (e.g. `user(id: 1)` and `user(id: 2)` without distinct aliases); fragments that select the same field with different arguments spread into the same scope; default arguments applied differently to two occurrences.

Common situations: Querying the same connection with different filters and forgetting distinct aliases; generated fragments (e.g. pagination or list fragments) reusing a field with varying arguments; copy-pasted selections where arguments were edited in one copy only.

Related errors

• fields of different type {type1} and {type2} cannot be merge
• '{alias:} is not a valid alias
• different fields {field1} and {field2} cannot be merged unde
• unable to fetch introspection schema: %w
• error in fetching introspection schema: %w

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/835271603be246ee. Report an issue: GitHub.