ModelBuilderExtensions.cs

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using System;
using System.ComponentModel.DataAnnotations;
using System.Linq.Expressions;
using System.Reflection;
 
using Microsoft.EntityFrameworkCore;
 
using Tgstation.Server.Api.Models;
 
namespace Tgstation.Server.Host.Extensions
{
    static class ModelBuilderExtensions
    {
        public static ModelBuilder MapMySqlTextField<TEntity>(
            this ModelBuilder modelBuilder,
            Expression<Func<TEntity, string?>> expression)
            where TEntity : class
        {
            var property = modelBuilder
                .Entity<TEntity>()
                .Property(expression);
            property
                .HasCharSet("utf8mb4");
 
            var propertyInfo = GetPropertyFromExpression(expression);
            var stringLengthAttribute = propertyInfo.GetCustomAttribute<StringLengthAttribute>();
 
            if (stringLengthAttribute?.MaximumLength == Limits.MaximumStringLength)
                property.HasColumnType("longtext");
 
            return modelBuilder;
        }
 
        static PropertyInfo GetPropertyFromExpression<TEntity>(Expression<Func<TEntity, string?>> expression)
        {
            MemberExpression memberExpression;
 
            // this line is necessary, because sometimes the expression comes in as Convert(originalexpression)
            if (expression.Body is UnaryExpression unaryExpression)
                if (unaryExpression.Operand is MemberExpression unaryAsMember)
                    memberExpression = unaryAsMember;
                else
                    throw new ArgumentException("Cannot get property from expression!", nameof(expression));
            else if (expression.Body is MemberExpression)
                memberExpression = (MemberExpression)expression.Body;
            else
                throw new ArgumentException("Cannot get property from expression!", nameof(expression));
 
            return (PropertyInfo)memberExpression.Member;
        }
    }
}