Goal - fill columns created dynamically. I cannot use a class with pre-created fields because, in my case, tags have to be found first.

Expectations:

excel:

{{model.name}} {{manufacturer.name}}

After processing:

A1 B1
A2 B2
A3 B3
A4 B4

Reality:

code:

var value = new Dictionary<string, object>
{
    ["model"] = new[]
    {
        new { name = "A1" },
        new { name = "A2" },
        new { name = "A3" },
        new { name = "A4" }
    },

    ["manufacturer"] = new[]
    {
        new { name = "B1" },
        new { name = "B2" },
        new { name = "B3" },
        new { name = "B4" },
    },
};

excel:

{{model.name}} {{manufacturer.name}}

Result:

B1 {{manufacturer.name}}
B2 {{manufacturer.name}}
B3 {{manufacturer.name}}
B4 {{manufacturer.name}}

Another approach through multiple SaveAsByTemplateAsync()

code:

MemoryStream memoryStream = new MemoryStream(0);

memoryStream.Write(bytes, 0, bytes.Length);

var value = new Dictionary<string, object>
{
    ["model"] = new[]
    {
        new { name = "A1" },
        new { name = "A2" },
        new { name = "A3" },
        new { name = "A4" }
    },
};

byte[] copiedData = memoryStream.ToArray();
await memoryStream.SaveAsByTemplateAsync(copiedData, value);

memoryStream.Position = 0;
MemoryStream clonedStream = new MemoryStream();
await memoryStream.CopyToAsync(clonedStream);
clonedStream.Position = 0;

await memoryStream.DisposeAsync();

byte[] copiedData1 = clonedStream.ToArray();

var value1 = new Dictionary<string, object>
{
    ["manufacturer"] = new[]
    {
        new { name = "B1" },
        new { name = "B2" },
        new { name = "B3" },
        new { name = "B4" }
    },
};

await clonedStream.SaveAsByTemplateAsync(copiedData1, value1);

Result:

A1 B1
A1 B2
A1 B3
A1 B4
A2 B1
A2 B2
A2 B3
A2 B4
A3 B1
A3 B2
A3 B3
A3 B4
A4 B1
A4 B2
A4 B3
A4 B4