Entity Framework and PostgreSQL: quotation marks issue

Easy done!

Go to OnModelCreating method.

You need an extension method (the code is shared below)

modelBuilder.NamesToSnakeCase();

Create ModelBuilderExtensions class and paste the following:

public static void NamesToSnakeCase(this ModelBuilder modelBuilder)
{
    foreach (var entity in modelBuilder.Model.GetEntityTypes())
    {
        // Replace table names
        entity.Relational().TableName = entity.Relational().TableName.ToSnakeCase();

        // Replace column names            
        foreach (var property in entity.GetProperties())
        {
            property.Relational().ColumnName = property.Name.ToSnakeCase();
        }

        foreach (var key in entity.GetKeys())
        {
            key.Relational().Name = key.Relational().Name.ToSnakeCase();
        }

        foreach (var key in entity.GetForeignKeys())
        {
            key.Relational().Name = key.Relational().Name.ToSnakeCase();
        }

        foreach (var index in entity.GetIndexes())
        {
            index.Relational().Name = index.Relational().Name.ToSnakeCase();
        }
    }
}

You can see ToSnakeCase extension method - here it is in StringExtensions class:

public static string ToSnakeCase(this string input)
{
    if (string.IsNullOrEmpty(input)) { return input; }

    var startUnderscores = Regex.Match(input, @"^_+");
    return startUnderscores + Regex.Replace(input, @"([a-z0-9])([A-Z])", "$1_$2").ToLower();
}

Remove the db, recreate migrations, then run dotnet ef database update - bingo!