[BUG]: non null string fails with InvalidDataException and is wrongly flagged as nullable

[ErikApption]

Library Version

4.25.0-pre.2

OS

Windows

OS Architecture

64 bit

How to reproduce?

1. Deserialize simple parquet file with schema (obtained from Tad - the parquet file also crashes floor)
   

2. "System.IO.InvalidDataException: 'property 'Value' is declared as 'value (System.String?)' but source data has it as 'value (System.String)''"

with

public class MyClass 
{
    [JsonPropertyName("id")]
    public long Id { get; set; }

    [JsonPropertyName("value")]
    public string Value { get; set; } = null!;

    [JsonPropertyName("frequency")]
    public double Frequency { get; set; }
}

The important part to note is that the exception is the same wherever Value is defined as nullable or not.

    [JsonPropertyName("value")]
    public string? Value { get; set; } = null!;

ends up with exactly same error message.

Failing test

var records = await ParquetSerializer.DeserializeAllAsync<MyClass>(stream).ToListAsync();

[aloneguid]

I'm not sure how to reproduce this to be honest, are you trying to deserialise a particular file with class serializer? Do you have a sample?

[ErikApption]

I'm not sure how to reproduce this to be honest, are you trying to deserialise a particular file with class serializer? Do you have a sample?

Yes I am trying to deserialize a class similar to PocoClassNotNullable using the class serializer.

I added unit tests in my PR to show the issue.

        class PocoClassNotNullable {
            [JsonPropertyName("id")]
            public long Id { get; set; }

            [JsonPropertyName("value")]
            public string Value { get; set; } = null!;

            [JsonPropertyName("frequency")]
            public double Frequency { get; set; }
        }

        [Fact]
        public void Strings_NotNullable() {
            ParquetSchema s = typeof(PocoClassNotNullable).GetParquetSchema(true);
            Assert.False(s.DataFields[0].IsNullable);
            Assert.False(s.DataFields[1].IsNullable);
            Assert.False(s.DataFields[2].IsNullable);
        }

This fails with current version and Value will be marked as IsNullable. The current code will consider any string as nullable (and Value above), so I don't think you can deserialize a non nullable string in parquet to a class unless you add [ParquetRequired] to that field. Without Roslyn annotations, there is no difference in metadata between string and string? - both are technically nullable because it is a class.

[ErikApption]

@aloneguid bumping this up - any chances you could look at my PR?