dotnet/efcore · error · InvalidOperationException

' . ' and ' . ' are both mapped to column ' ' in ' ', but…

Error message

'{entityType1}.{property1}' and '{entityType2}.{property2}' are both mapped to column '{columnName}' in '{table}', but are configured to use different collations ('{collation1}' and '{collation2}').

What it means

Two properties sharing a column declare different collations via HasCollation / UseCollation. A physical column has exactly one collation; conflicting settings would produce contradictory ALTER COLUMN statements, so EF rejects the model. Compared with StringComparison.Ordinal (case-sensitive).

Solutions

Apply the same HasCollation("...") to both properties (exact case match).
Remove HasCollation from one side so both inherit the database/column default.
If collations truly must differ, remap one property to its own column.

Example fix

// before
modelBuilder.Entity<User>().Property(u => u.UserName).UseCollation("SQL_Latin1_General_CP1_CI_AS");
modelBuilder.Entity<UserProfile>().Property(p => p.UserName).UseCollation("SQL_Latin1_General_CP1_CS_AS"); // shared

// after
modelBuilder.Entity<User>().Property(u => u.UserName).UseCollation("SQL_Latin1_General_CP1_CI_AS");
modelBuilder.Entity<UserProfile>().Property(p => p.UserName).UseCollation("SQL_Latin1_General_CP1_CI_AS");

Defensive patterns

Strategy: validation

Validate before calling

foreach (var (col, props) in sharedColumnGroups)
{
    var collations = props.Select(p => p.GetCollation(storeObject) ?? "").Distinct(StringComparer.Ordinal).ToList();
    if (collations.Count > 1)
        Console.WriteLine($"Column {col} has conflicting collations: {string.Join(", ", collations)}");
}

Try / catch

try { _ = db.Model; } catch (InvalidOperationException ex) when (ex.Message.Contains("different collations")) { // align UseCollation/HasCollation on both properties }

Prevention

Decide on one collation per shared string column and apply it everywhere.
Remember collation names compare case-sensitively; copy the exact name.
Smoke-test the model at startup.

When it happens

Trigger: ValidateCompatible() reads property.GetCollation(storeObject) and duplicateProperty.GetCollation(storeObject) (null coerced to empty); if they differ under Ordinal it throws. Common on string columns shared between entities.

Common situations: Case-sensitive vs case-insensitive collation mismatch ('SQL_Latin1_General_CP1_CI_AS' vs '..._CS_AS'); cross-database or cross-column collation applied inconsistently; scaffold then partial manual collation edits.

Related errors

AI-assisted analysis of dotnet/efcore@3a2006ef56 (2026-08-11). Data as JSON: /api/errors/e769ecbf282338a3. Report an issue: GitHub.

Appendix: source

Thrown at src/EFCore.Relational/Infrastructure/RelationalModelValidator.cs:1764

        if (!currentComment.Equals(previousComment, StringComparison.Ordinal))
        {
            throw new InvalidOperationException(
                RelationalStrings.DuplicateColumnNameCommentMismatch(
                    duplicateProperty.DeclaringType.DisplayName(),
                    duplicateProperty.Name,
                    property.DeclaringType.DisplayName(),
                    property.Name,
                    columnName,
                    storeObject.DisplayName(),
                    previousComment,
                    currentComment));
        }

        var currentCollation = property.GetCollation(storeObject) ?? "";
        var previousCollation = duplicateProperty.GetCollation(storeObject) ?? "";
        if (!currentCollation.Equals(previousCollation, StringComparison.Ordinal))
        {
            throw new InvalidOperationException(
                RelationalStrings.DuplicateColumnNameCollationMismatch(
                    duplicateProperty.DeclaringType.DisplayName(),
                    duplicateProperty.Name,
                    property.DeclaringType.DisplayName(),
                    property.Name,
                    columnName,
                    storeObject.DisplayName(),
                    previousCollation,
                    currentCollation));
        }

        var currentColumnOrder = property.GetColumnOrder(storeObject);
        var previousColumnOrder = duplicateProperty.GetColumnOrder(storeObject);
        if (currentColumnOrder != previousColumnOrder)
        {
            throw new InvalidOperationException(
                RelationalStrings.DuplicateColumnNameOrderMismatch(
                    duplicateProperty.DeclaringType.DisplayName(),

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