DapperLib / DapperLib/Dapper.Contrib

MySqlAdapter InsertAsync unexpectedly modifies entityToInsert

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Dominant language
C#
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Description

We are writing our code entirely with immutable objects. The benefits are, that a quite substancial class of programmer errors are simply excluded. Now when saving such an immutable dto to the mySql database, we are getting an System.ArgumentException : Property set method not found. exception.
It seems that MySqlAdapter tries to update the key property with the newly generated key value from the database here:
` public async Task InsertAsync(IDbConnection connection, IDbTransaction transaction, int? commandTimeout, string tableName,
string columnList, string parameterList, IEnumerable keyProperties, object entityToInsert)
{
var cmd = $"INSERT INTO {tableName} ({columnList}) VALUES ({parameterList})";
await connection.ExecuteAsync(cmd, entityToInsert, transaction, commandTimeout).ConfigureAwait(false);
var r = await connection.QueryAsync("SELECT LAST_INSERT_ID() id", transaction: transaction, commandTimeout: commandTimeout).ConfigureAwait(false);

    var id = r.First().id;
    if (id == null) return 0;
    var pi = keyProperties as PropertyInfo[] ?? keyProperties.ToArray();
    if (pi.Length == 0) return Convert.ToInt32(id);

    var idp = pi[0];
    idp.SetValue(entityToInsert, Convert.ChangeType(id, idp.PropertyType), null);

    return Convert.ToInt32(id);
}

`
This is really sad because it not only makes it impossible to use immutable dtos but also hinders usage of non db generated keys such as GUIDs.

In my opinion, these lines should be removed entirely, as it is not the responsability of the InsertAsync method to modify the dto that is being inserted:
var pi = keyProperties as PropertyInfo[] ?? keyProperties.ToArray(); if (pi.Length == 0) return Convert.ToInt32(id); var idp = pi[0]; idp.SetValue(entityToInsert, Convert.ChangeType(id, idp.PropertyType), null);

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start at MySqlAdapter.InsertAsync and inspect how keyProperties and entityToInsert are used. Reproduce the Property set method not found exception with an immutable DTO, then verify that insertion no longer attempts to mutate the inserted entity and that non-database-generated keys remain usable.

Written by the indexing model from the issue text.

Assessment

Tech stack
csharp, mysql
Domain
databases
Issue type
Bug
Difficulty
2/5
Estimated time
1-3 hours
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
52/100

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