LuckyPennySoftware/AutoMapper · error · InvalidOperationException

Not enough room in destination array {destination}

Error message

Not enough room in destination array {destination}

What it means

Maps a flat source collection into a multidimensional (ranked) destination array via MultidimensionalArrayFiller, filling cells dimension by dimension. The throw fires when the dimension counter walks past every dimension (dimension < 0) while NewValue still has elements to place, i.e. the source holds more values than the destination array's total cell capacity. It is the library's way of refusing a silent truncation when shapes do not match.

Source

Thrown at src/AutoMapper/Mappers/CollectionMapper.cs:260

            bool MustMap(Type sourceType, Type destinationType) => !destinationType.IsAssignableFrom(sourceType) ||
                configuration.FindTypeMapFor(sourceType, destinationType) != null;
        }
    }
}
public readonly struct MultidimensionalArrayFiller(Array destination)
{
    readonly int[] _indices = new int[destination.Rank];
    public void NewValue(object value)
    {
        var dimension = destination.Rank - 1;
        var changedDimension = false;
        while (_indices[dimension] == destination.GetLength(dimension))
        {
            _indices[dimension] = 0;
            dimension--;
            if (dimension < 0)
            {
                throw new InvalidOperationException("Not enough room in destination array " + destination);
            }
            _indices[dimension]++;
            changedDimension = true;
        }
        destination.SetValue(value, _indices);
        if (changedDimension)
        {
            _indices[dimension + 1]++;
        }
        else
        {
            _indices[dimension]++;
        }
    }
}

View on GitHub (pinned to dfa6dd587c)

Solutions

1. Size the destination multidimensional array so the product of all GetLength(d) is >= source element count before mapping.
2. Trim or page the source collection so its count fits the fixed destination shape.
3. Switch the destination to a 1D array or List<T> when the multidimensional shape is not actually required.
4. Pre-validate dimensions against the source and surface a domain error instead of letting AutoMapper throw.

Example fix

// before
var dest = new int[2, 2];
mapper.Map(srcList, dest); // throws if srcList.Count > 4

// after
var rows = (int)Math.Ceiling(Math.Sqrt(srcList.Count));
var dest = new int[rows, srcList.Count % rows == 0 ? srcList.Count / rows : srcList.Count / rows + 1];
mapper.Map(srcList, dest);

static long ArrayCapacity(Array a)
{
    long capacity = 1;
    for (int d = 0; d < a.Rank; d++) capacity *= a.GetLength(d);
    return capacity;
}

long needed = source.Cast<object>().LongCount();
if (needed > ArrayCapacity(destination))
    throw new ArgumentException($"Destination array capacity ({ArrayCapacity(destination)}) < source count ({needed}).");

mapper.Map(source, destination);

try { mapper.Map(source, destination); }
catch (InvalidOperationException ex) when (ex.Message.Contains("Not enough room in destination array"))
{
    // recompute destination dimensions or trim the source, then retry once
}

When it happens

Trigger: Calling Map from an IEnumerable/array onto a System.Array with Rank > 1 (e.g. int[,], string[,,]) where source.Count() exceeds the product of destination.GetLength(d) over all d. Each source element invokes MultidimensionalArrayFiller.NewValue, so one extra element after the last cell is full triggers the throw.

Common situations: Destination array allocated with stale/wrong dimension lengths after the source grew; off-by-one when sizing dims at runtime; data import where row/column counts exceed the pre-allocated matrix; reusing a fixed-size buffer for variable-size input.

AI-assisted analysis of LuckyPennySoftware/AutoMapper@dfa6dd587c (2026-08-13). Data as JSON: /api/errors/257c602e4ab0cc84. Report an issue: GitHub.