dotnet/efcore · error · InvalidOperationException

The parameter for the property '{property}' cannot be added

Error message

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

What it means

Thrown by StoredProcedure.AddParameter when a current-value parameter for the given property name is already present in _currentValueParameters. Each property can have at most one current-value parameter on a stored procedure.

Source

Thrown at src/EFCore.Relational/Metadata/Internal/StoredProcedure.cs:513

    ///     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 StoredProcedureParameter? FindParameter(string propertyName)
        => _currentValueParameters.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 StoredProcedureParameter AddParameter(string propertyName)
    {
        if (_currentValueParameters.ContainsKey(propertyName))
        {
            throw new InvalidOperationException(
                RelationalStrings.StoredProcedureDuplicateParameter(
                    propertyName, ((IReadOnlyStoredProcedure)this).GetStoreIdentifier()?.DisplayName()));
        }

        var parameter = new StoredProcedureParameter(this, rowsAffected: false, propertyName, originalValue: false);
        _parameters.Add(parameter);
        _currentValueParameters.Add(propertyName, parameter);

        return parameter;
    }

    /// <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 StoredProcedureParameter? FindOriginalValueParameter(string propertyName)

View on GitHub (pinned to dbf9771522)

Solutions

1. Guard with FindParameter(propertyName) before calling AddParameter.
2. Remove the duplicate .Parameter/.AddParameter call for the same property.
3. If reconfiguring, call the builder only once per property.

Example fix

// before
s.AddParameter("Name");
s.AddParameter("Name"); // throws

// after
if (s.FindParameter("Name") == null) s.AddParameter("Name");

static StoredProcedureParameter AddParameterOnce(StoredProcedure sproc, string propertyName)
    => sproc.FindParameter(propertyName) ?? sproc.AddParameter(propertyName);

When it happens

Trigger: StoredProcedure.cs:511-516: _currentValueParameters.ContainsKey(propertyName) is true. Produced by calling .AddParameter("X") twice, or by EF automatically adding a parameter and then user code adding it again.

Common situations: Calling .Parameter(x => x.Name) twice; mixing the lambda and string overloads for the same property; scaffolding a sproc and then re-adding parameters manually.

Related errors

• The original value parameter for the property '{property}' c
• The rows affected parameter cannot be added to the stored pr
• The result column for the property '{property}' cannot be ad
• The rows affected result column cannot be added to the store
• '{facet}' cannot be configured for the parameter '{parameter

AI-assisted analysis of dotnet/efcore@dbf9771522 (2026-08-06). Data as JSON: /api/errors/d6583fcbb8273333. Report an issue: GitHub.