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https://issues.apache.org/jira/browse/AVRO-4054?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17880787#comment-17880787
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Zoltan Csizmadia edited comment on AVRO-4054 at 9/10/24 9:06 PM:
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If you create your own writer based on DefaultWriter, you can override the
WriteMap call.
{code:java}
class MyDefaultWriter : DefaultWriter
{
public MyDefaultWriter(Schema schema) : base(schema)
{
}
protected override void WriteMap(MapSchema schema, object value, Encoder
encoder)
{
var map = value as System.Collections.IDictionary;
if (map == null)
{
throw new AvroTypeException("Map does not implement non-generic
IDictionary");
}
encoder.WriteMapStart();
encoder.SetItemCount(map.Count);
foreach (System.Collections.DictionaryEntry de in map)
{
encoder.StartItem();
encoder.WriteString(de.Key as string);
Write(schema.ValueSchema, de.Value, encoder);
}
encoder.WriteMapEnd();
}
}
...
var schema = MapSchema.CreateMap(PrimitiveSchema.Create(Schema.Type.Long));
var ms = new MemoryStream();
BinaryEncoder enc = new BinaryEncoder(ms);
var writer = new MyDefaultWriter(schema);
writer.Write(new Dictionary<string, long>(), enc);
enc.Flush();{code}
was (Author: [email protected]):
If you create your own writer based on DefaultWriter, you can override the
WriteMap call.
{code:java}
class MyDefaultWriter : DefaultWriter
{
public MyDefaultWriter(Schema schema) : base(schema)
{
}
protected override void WriteMap(MapSchema schema, object value, Encoder
encoder)
{
var map = value as System.Collections.IDictionary;
if (map == null)
{
throw new AvroTypeException("Map does not implement non-generic
IDictionary");
} encoder.WriteMapStart();
encoder.SetItemCount(map.Count);
foreach (System.Collections.DictionaryEntry de in map)
{
encoder.StartItem();
encoder.WriteString(de.Key as string);
Write(schema.ValueSchema, de.Value, encoder);
}
encoder.WriteMapEnd();
}
}
...
var schema = MapSchema.CreateMap(PrimitiveSchema.Create(Schema.Type.Long));
var ms = new MemoryStream();
BinaryEncoder enc = new BinaryEncoder(ms);
var writer = new MyDefaultWriter(schema);
writer.Write(new Dictionary<string, long>(), enc);
enc.Flush();{code}
> Serialization of C# Dictionary only works if type is <string, object>
> ---------------------------------------------------------------------
>
> Key: AVRO-4054
> URL: https://issues.apache.org/jira/browse/AVRO-4054
> Project: Apache Avro
> Issue Type: Bug
> Components: csharp
> Affects Versions: 1.12.0
> Environment: I was testing this in a .Net Standard 2.0 project.
> Reporter: Rob Komjathy
> Priority: Major
>
> I encountered an unexpected behavior with Avro Maps (C# Dictionaries). If I
> directly try to serialize a Dictionary<string, T> where T is any type besides
> literally "object", an exception is thrown.
> If you dig into the code, it's because you can't directly cast
> Dictionary<string, T> to Dictionary<string, object>. This fails on at least
> 3 lines in DefaultWriter, as there are several attempts made to verify the
> Dictionary "is" <string, object> or can be cast to it directly.
> For example, here is a rudimentary example.
>
> {code:java}
> var schema = MapSchema.CreateMap(PrimitiveSchema.Create(Schema.Type.Long));
> var ms = new MemoryStream();
> Encoder enc = new BinaryEncoder(ms);
> var writer = new DefaultWriter(schema);
> writer.Write(new Dictionary<string, long>(), enc);
> enc.Flush(); {code}
> Given this example, I would expect to be able to pass a Dictionary<string,
> long> given the schema I have defined. Instead this throws an exception.
>
> The work around is to create a new Dictionary<string, object> and
> individually cast the values to "objects". For example:
>
> {code:java}
> public static Dictionary<string, object> ToAvroSafeDictionary<TValue>(this
> IDictionary<string, TValue> dictionary)
> {
> return dictionary?.ToDictionary(k => k.Key, v => (object)v.Value);
> } {code}
> I originally encountered this with my own custom schema but as you can see,
> using Apache Avro's own schema objects in the rudimentary example exhibit the
> same issue.
>
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