DapperLib/Dapper · error · NotSupportedException

The type '{value.GetType().Name}' is not supported for SQL l

Error message

The type '{value.GetType().Name}' is not supported for SQL literals.

What it means

Thrown by `SqlMapper.Format(object?)` when a value used in a literal substitution (`{=name}`) is of a type Dapper will not inline as a SQL literal. Format only inlines numeric primitives (bool, byte/sbyte, ushort/short, uint/int, ulong/long, float, double, decimal) and recursively-formatted enumerables of those; everything else — strings, DateTime, Guid, TimeSpan, char, enums of non-int backing, custom types — falls through to NotSupportedException. This is intentional: inlining strings/dates would risk SQL injection.

Source

Thrown at Dapper/SqlMapper.cs:2504

                                    sb = GetStringBuilder().Append('(');
                                    first = false;
                                }
                                else
                                {
                                    sb!.Append(',');
                                }
                                sb.Append(Format(subval));
                            }
                            if (first)
                            {
                                return "(select null where 1=0)";
                            }
                            else
                            {
                                return sb!.Append(')').ToStringRecycle();
                            }
                        }
                        throw new NotSupportedException($"The type '{value.GetType().Name}' is not supported for SQL literals.");
                }
            }
        }

        internal static void ReplaceLiterals(IParameterLookup parameters, IDbCommand command, IList<LiteralToken> tokens)
        {
            var sql = command.CommandText;
            foreach (var token in tokens)
            {
                object? value = parameters[token.Member];
#pragma warning disable 0618
                string text = Format(value);
#pragma warning restore 0618
                sql = sql.Replace(token.Token, text);
            }
            command.CommandText = sql;
        }

View on GitHub (pinned to 72a54c475f)

Solutions

1. Use a normal parameter (`@name`) instead of `{=name}` for strings, dates, Guids, and other non-numeric values.
2. If you must inline a date/guid, pre-format it to a SQL-safe string literal yourself and only then use it (with extreme care), or keep it parameterized.
3. Register a custom literal type handler / convert the value to a supported primitive before substitution.
4. Double-check that the literal token points at a numeric column/value.

Example fix

// before (DateTime not supported as literal)
var sql = "select * from t where created = {=AsOf}";
var rows = cnn.Query<T>(sql, new { AsOf = DateTime.UtcNow });
// after
var sql = "select * from t where created = @AsOf";
var rows = cnn.Query<T>(sql, new { AsOf = DateTime.UtcNow });

// Only inline numeric literals with {=}; parameterize everything else.
var sql = isNumeric ? $"... {=Value}" : "... @Value";

static bool IsLiteralSafe(object? v) => v is bool or byte or sbyte or short or ushort or int or uint or long or ulong or float or double or decimal;

When it happens

Trigger: Using the literal syntax `where created = {=Created}` where `Created` is a DateTime, or `where name = {=Name}` where Name is a string; passing a Guid, TimeSpan, or a custom struct to a `{=...}` token. The token is resolved by ReplaceLiterals (SqlMapper.cs:2509) which calls Format on the member value.

Common situations: Confusing literal substitution `{=x}` (safe only for numbers) with normal parameterization `@x`; trying to inline a date or GUID for a provider that needs it inlined; using `{=}` on a string for convenience.

Related errors

• A single-character was expected
• An item with the same key has already been added
• type
• This operation requires an identity or a connected command
• type

AI-assisted analysis of DapperLib/Dapper@72a54c475f (2026-08-13). Data as JSON: /api/errors/8ed35d9f3a0fd168. Report an issue: GitHub.