dotnet/efcore · error · InvalidOperationException

The result column for the property

Error message

The result column for the property '{property}' cannot be added to the stored procedure '{sproc}' because another result column for this property already exists.

What it means

A stored procedure cannot project the same property into two result columns. AddResultColumn(propertyName) throws when _propertyResultColumns already contains that property name, since each mapped property may contribute at most one output column.

Solutions

Call FindResultColumn(propertyName) before adding; only add when it returns null.
Remove the duplicate .ResultColumn(propertyName) call.
If the property is store-generated, let conventions create the result column and do not add it manually.
Audit each procedure's GetResultColumns() to confirm no duplicates before fluent configuration.

Example fix

// before
sp.ResultColumn("RowVersion");
sp.ResultColumn("RowVersion"); // throws: duplicate

// after
if (sp.FindResultColumn("RowVersion") is null)
{
    sp.ResultColumn("RowVersion");
}

Defensive patterns

Strategy: validation

Validate before calling

// Add a result column only if no column exists for that property.
if (sp.FindResultColumn(propertyName) is null)
{
    sp.ResultColumn(propertyName);
}

Type guard

static bool CanAddResultColumn(IStoredProcedure sp, string propertyName)
    => sp.FindResultColumn(propertyName) is null;

Prevention

Build a small wrapper that checks FindResultColumn before adding.
Avoid manually adding result columns for store-generated properties that conventions already map.
Unit-test procedure configurations against the finalized model.

When it happens

Trigger: Calling .ResultColumn("CreatedAt") twice on the same procedure, or calling it once explicitly when convention/attribute mapping already added a result column for that property (e.g. a computed property auto-mapped as a result column).

Common situations: Adding explicit result columns on top of auto-discovered ones after an EF Core upgrade changed convention behavior; shared fluent code between insert and update procedures where the same property is re-listed; mapping a store-generated (computed/default) property that conventions already treat as a result column.

Related errors

AI-assisted analysis of dotnet/efcore@3a2006ef56 (2026-08-11). Data as JSON: /api/errors/7248799d9e3d3778. Report an issue: GitHub.

Appendix: source

Thrown at src/EFCore.Relational/Metadata/Internal/StoredProcedure.cs:620

    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
    ///     any release. You should only use it directly in your code with extreme caution and knowing that
    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
    /// </summary>
    public virtual StoredProcedureResultColumn? FindResultColumn(string propertyName)
        => _propertyResultColumns.GetValueOrDefault(propertyName);

    /// <summary>
    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
    ///     any release. You should only use it directly in your code with extreme caution and knowing that
    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
    /// </summary>
    public virtual StoredProcedureResultColumn AddResultColumn(string propertyName)
    {
        if (_propertyResultColumns.ContainsKey(propertyName))
        {
            throw new InvalidOperationException(
                RelationalStrings.StoredProcedureDuplicateResultColumn(
                    propertyName, ((IReadOnlyStoredProcedure)this).GetStoreIdentifier()?.DisplayName()));
        }

        var resultColumn = new StoredProcedureResultColumn(this, forRowsAffected: false, propertyName);
        _resultColumns.Add(resultColumn);
        _propertyResultColumns.Add(propertyName, resultColumn);

        return resultColumn;
    }

    /// <summary>
    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
    ///     any release. You should only use it directly in your code with extreme caution and knowing that
    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
    /// </summary>
    public virtual StoredProcedureResultColumn? FindRowsAffectedResultColumn()

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