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Azure Storage exception when a string length is more than 32768 characters

由 青春壹個敷衍的年華 提交于 2019-12-01 09:22:29

You are encountered the Azure Storage limit for the string property type (source):

Edm.String (String) - A UTF-16-encoded value. String values may be up to 64 KB in size.

Because UTF-16 encoded strings require 2 bytes to store an character the maximum string length is 32768 characters.

Though this has already been answered, I'd like to propose solution for anyone else who might come across this thread. I needed to store significantly more than 64k in a single property in my table entity. I found several references online to Lokad Fat Entities, however, it seems it is no longer actively supported and I had runtime errors with the version available on NuGet.org. So, here is a class that is inspired by Lokad's solution. I hope others find it useful.

    public class ExtEntity<T> : TableEntity where T : new()
{
    private const int MAX_BYTES_PER_ARR = 65500; // don't use full 64k to avoid any weird edge case

    // Serialized in DB and deserialized for callers
    public Byte[] A0 { get; set; }
    public Byte[] A1 { get; set; }
    public Byte[] A2 { get; set; }
    public Byte[] A3 { get; set; }
    public Byte[] A4 { get; set; }
    public Byte[] A5 { get; set; }
    public Byte[] A6 { get; set; }
    public Byte[] A7 { get; set; }
    public Byte[] A8 { get; set; }
    public Byte[] A9 { get; set; }
    public Byte[] A10 { get; set; }
    public Byte[] A11 { get; set; }
    public Byte[] A12 { get; set; }
    public Byte[] A13 { get; set; }
    public Byte[] A14 { get; set; }
    public Byte[] A15 { get; set; }
    private T value;

    public T Value
    {
        // Accessors automatically serialize and deserialize T value
        get
        {
            // ASSUMES that value will never change after first time deserialized!
            if (this.value == null)
            {
                int n = 0;
                using (var memStream = new MemoryStream())
                {
                    while (true)
                    {
                        string propName = "A" + n++;
                        PropertyInfo prop = this.GetType().GetProperty(propName);
                        byte[] arr = (byte[])prop.GetValue(this);
                        if (arr == null || arr.Length == 0)
                        {
                            break;
                        }
                        memStream.Write(arr, 0, arr.Length);
                    }
                    memStream.Seek(0, SeekOrigin.Begin);
                    var binForm = new BinaryFormatter();
                    this.value = (T)binForm.Deserialize(memStream);
                }
            }
            return this.value;
        }
        set
        {
            // First, ensure the type is serializable.
            if (!typeof(T).IsSerializable && !(typeof(ISerializable).IsAssignableFrom(typeof(T))))
                throw new InvalidOperationException("ExtEntity<T>.get_Value Exception: A serializable Type is required.");

            // Assign the value
            this.value = value;

            // Then searialize it for Table Storage use
            BinaryFormatter bf = new BinaryFormatter();
            using (var memStream = new MemoryStream())
            {
                // Serialize into memory stream, then seek back to origin
                bf.Serialize(memStream, this.value);
                memStream.Seek(0, SeekOrigin.Begin);

                // Chunk data from memory stream into stored properties
                int bytesRemaining = (int)memStream.Length;
                int n = 0;
                while (bytesRemaining > 0)
                {
                    if (n > 15)
                    {
                        throw new ApplicationException("ExtEntity<T>.set_Value Exception: Data is too large.");
                    }
                    int numToRead = Math.Min(bytesRemaining, ExtEntity<T>.MAX_BYTES_PER_ARR);
                    byte[] arr = new byte[numToRead];
                    int numRead = memStream.Read(arr, 0, numToRead);
                    if (numRead != numToRead)
                    {
                        throw new ApplicationException("ExtEntity<T>.set_Value Exception: Unexpected number of bytes returned.");
                    }

                    string propName = "A" + n++;
                    PropertyInfo prop = this.GetType().GetProperty(propName);
                    prop.SetValue(this, arr);
                    bytesRemaining -= numRead;
                }
            }
        }
    }
}

Sample usage:

public class RawDataBlockEntity : ExtEntity<RawDataBlock>
{
    public RawDataBlockEntity(string rawDataId, string blockId, RawDataBlock block)
    {
        this.PartitionKey = rawDataId;
        this.RowKey = blockId;

        this.Value = block;
    }

    public RawDataBlockEntity() { }
}

Try this:

return new ContentResult { Content = this.GetResponse(), StatusCode = 200 };
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c#
ASP.NET
azure
asp.net-core
azure-table-storage
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