Implementation of parameterized sql queries using string interpolation handlers

FromSqlInterpolatedStringHandler.cs

using System.Data.Common;
using System.Runtime.CompilerServices;
using System.Text;
using Npgsql;

GetCatalogItemsSql(null, null, null, 10);

void GetCatalogItemsSql(int? catalogBrandId, int? before, int? after, int pageSize)
{
    // This looks like it would be susceptible to SQL injection, but it's not.
    // The interpolated string is converted to a FromSqlInterpolatedStringHandler which will turn those
    // interpolated values in to parameterized values.

    SqlQuery($"""
    SELECT *
    FROM "Catalog" AS c
    WHERE ({catalogBrandId} IS NULL OR c."CatalogBrandId" = {catalogBrandId})
    AND ({before} IS NULL OR c."Id" < {before})
    AND ({after} IS NULL OR c."Id" >= {after})
    ORDER BY c."Id"
    LIMIT {pageSize + 1}
    """);

}

void SqlQuery(in FromSqlInterpolatedStringHandler builder)
{
    Console.WriteLine(builder.GetQueryText());
    Console.WriteLine();
    foreach (var p in builder.GetParameters())
    {
        Console.WriteLine($"{p.ParameterName} = {(p.Value is null ? "NULL" : p.Value.ToString())}");
    }
}


[InterpolatedStringHandler]
public ref struct FromSqlInterpolatedStringHandler
{
    StringBuilder _builder;
    int _paramterCount;
    DbParameter[]? _parameters;

    public FromSqlInterpolatedStringHandler(int literalLength, int formattedCount)
    {
        _builder = new StringBuilder(literalLength);
        _parameters = formattedCount > 0 ? new DbParameter[formattedCount] : null;
    }

    public void AppendLiteral(string s)
    {
        _builder.Append(s);
    }

    public void AppendFormatted<T>(T t)
    {
        var parameterName = $"@p{_paramterCount}";
        _builder.Append(parameterName);
        _parameters![_paramterCount++] = new NpgsqlParameter<T>(parameterName, t);
    }

    internal string GetQueryText() => _builder.ToString();

    internal DbParameter[] GetParameters() => _parameters ?? Array.Empty<DbParameter>();
}