QueryableProvider.cs

using FreeSql.Internal;
using FreeSql.Internal.CommonProvider;
using FreeSql.Internal.Model;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Text;

namespace FreeSql.Extensions.Linq
{
    class QueryableProvider<TCurrent, TSource> : IQueryable<TCurrent>, IOrderedQueryable<TCurrent> where TSource : class
    {
        Expression _expression;
        IQueryProvider _provider;
        internal Select1Provider<TSource> _select;

        public QueryableProvider(Select1Provider<TSource> select)
        {
            _select = select;
            _expression = Expression.Constant(this);
            _provider = new QueryProvider<TCurrent, TSource>(_select, _expression);
        }
        public QueryableProvider(Expression expression, IQueryProvider provider, Select1Provider<TSource> select)
        {
            _select = select;
            _expression = expression;
            _provider = provider;
        }

        public IEnumerator<TCurrent> GetEnumerator()
        {
            var result = _provider.Execute<List<TCurrent>>(_expression);
            if (result == null)
                yield break;
            foreach (var item in result)
            {
                yield return item;
            }
        }
        IEnumerator IEnumerable.GetEnumerator()
        {
            return (IEnumerator)GetEnumerator();
        }

        public Type ElementType => typeof(QueryableProvider<TCurrent, TSource>);
        public Expression Expression => _expression;
        public IQueryProvider Provider => _provider;
    }

    class QueryProvider<TCurrent, TSource> : IQueryProvider where TSource : class
    {
        Select1Provider<TSource> _select;
        Expression _oldExpression;

        public QueryProvider(Select1Provider<TSource> select, Expression oldExpression)
        {
            _select = select;
            _oldExpression = oldExpression;
        }

        public IQueryable<TElement> CreateQuery<TElement>(Expression expression)
        {
            ExecuteExp(expression, null, false);
            if (typeof(TElement) != typeof(TCurrent))
                return new QueryableProvider<TElement, TSource>(expression, new QueryProvider<TElement, TSource>(_select, expression), _select);

            _oldExpression = expression;
            return new QueryableProvider<TElement, TSource>(expression, this, _select);
        }
        public IQueryable CreateQuery(Expression expression) => throw new NotImplementedException();

        public TResult Execute<TResult>(Expression expression)
        {
            return (TResult)ExecuteExp(expression, typeof(TResult), _oldExpression == expression);
        }
        public object Execute(Expression expression) => throw new NotImplementedException();

        public object ExecuteExp(Expression expression, Type tresult, bool isProcessed)
        {
            var callExp = expression as MethodCallExpression;
            var isfirst = false;
            if (callExp != null && isProcessed == false)
            {
                object throwCallExp(string message) => throw new Exception($"解析失败 {callExp.Method.Name} {message}，提示：可以使用扩展方法 IQueryable.RestoreToSelect() 还原为 ISelect 再查询");
                if (callExp.Method.DeclaringType != typeof(Queryable)) return throwCallExp($"必须属于 System.Linq.Queryable");

                object tplMaxMinAvgSum(string method)
                {
                    if (callExp.Arguments.Count == 2)
                    {
                        var avgParam = (callExp.Arguments[1] as UnaryExpression)?.Operand as LambdaExpression;
                        return Utils.GetDataReaderValue(tresult,
                            _select.GetType().GetMethod(method).MakeGenericMethod(avgParam.ReturnType).Invoke(_select, new object[] { avgParam }));
                    }
                    return throwCallExp($" 不支持 {callExp.Arguments.Count}个参数的方法");
                }
                object tplOrderBy(string method, bool isDescending)
                {
                    if (callExp.Arguments.Count == 2)
                    {
                        var arg1 = (callExp.Arguments[1] as UnaryExpression)?.Operand as LambdaExpression;
                        _select.OrderByReflection(arg1, isDescending);
                        return tresult.CreateInstanceGetDefaultValue();
                    }
                    return throwCallExp($" 不支持 {callExp.Arguments.Count}个参数的方法");
                }
                switch (callExp.Method.Name)
                {
                    case "Any":
                        if (callExp.Arguments.Count == 2) _select.InternalWhere(callExp.Arguments[1]);
                        return _select.Any();
                    case "AsQueryable":
                        break;

                    case "Max": return tplMaxMinAvgSum("Max");
                    case "Min": return tplMaxMinAvgSum("Min");
                    case "Sum": return tplMaxMinAvgSum("Sum");
                    case "Average": return tplMaxMinAvgSum("Avg");

                    case "Concat":
                        return throwCallExp(CoreErrorStrings.Not_Support);
                    case "Contains":
                        if (callExp.Arguments.Count == 2)
                        {
                            var dywhere = callExp.Arguments[1].GetConstExprValue();
                            if (dywhere == null) return throwCallExp($" 参数值不能为 null");
                            _select.WhereDynamic(dywhere);
                            return _select.Any();
                        }
                        return throwCallExp($" 不支持 {callExp.Arguments.Count}个参数的方法");
                    case "Count":
                        if (callExp.Arguments.Count == 2) _select.InternalWhere(callExp.Arguments[1]);
                        return Utils.GetDataReaderValue(tresult, _select.Count());

                    case "Distinct":
                        if (callExp.Arguments.Count == 1)
                        {
                            _select.Distinct();
                            break;
                        }
                        return throwCallExp(CoreErrorStrings.Not_Support);

                    case "ElementAt":
                    case "ElementAtOrDefault":
                        _select.Offset((int)callExp.Arguments[1].GetConstExprValue());
                        _select.Limit(1);
                        isfirst = true;
                        break;
                    case "First":
                    case "FirstOrDefault":
                    case "Single":
                    case "SingleOrDefault":
                        if (callExp.Arguments.Count == 2) _select.InternalWhere(callExp.Arguments[1]);
                        _select.Limit(1);
                        isfirst = true;
                        break;

                    case "OrderBy":
                        tplOrderBy("OrderByReflection", false);
                        break;
                    case "OrderByDescending":
                        tplOrderBy("OrderByReflection", true);
                        break;
                    case "ThenBy":
                        tplOrderBy("OrderByReflection", false);
                        break;
                    case "ThenByDescending":
                        tplOrderBy("OrderByReflection", true);
                        break;

                    case "Where":
                        var whereParam = (callExp.Arguments[1] as UnaryExpression)?.Operand as LambdaExpression;
                        if (whereParam.Parameters.Count == 1)
                        {
                            _select.InternalWhere(whereParam);
                            break;
                        }
                        return throwCallExp(CoreErrorStrings.Not_Support);

                    case "Skip":
                        _select.Offset((int)callExp.Arguments[1].GetConstExprValue());
                        break;
                    case "Take":
                        _select.Limit((int)callExp.Arguments[1].GetConstExprValue());
                        break;

                    case "ToList":
                        if (callExp.Arguments.Count == 1)
                            return _select.ToList();
                        return throwCallExp(CoreErrorStrings.Not_Support);

                    case "Select":
                        var selectParam = (callExp.Arguments[1] as UnaryExpression)?.Operand as LambdaExpression;
                        if (selectParam.Parameters.Count == 1)
                        {
                            _select._selectExpression = selectParam;
                            break;
                        }
                        return throwCallExp(CoreErrorStrings.Not_Support);

                    case "Join":
                        if (callExp.Arguments.Count == 5)
                        {
                            var arg2 = (callExp.Arguments[2] as UnaryExpression)?.Operand as LambdaExpression;
                            var arg3 = (callExp.Arguments[3] as UnaryExpression)?.Operand as LambdaExpression;
                            var arg4 = (callExp.Arguments[4] as UnaryExpression)?.Operand as LambdaExpression;
                            FreeSqlExtensionsLinqSql.InternalJoin2(_select, arg2, arg3, arg4);
                            _select._selectExpression = arg4.Body;
                            break;
                        }
                        return throwCallExp($" 不支持 {callExp.Arguments.Count}个参数的方法");

                    case "GroupJoin":
                        if (callExp.Arguments.Count == 5)
                        {
                            var arg2 = (callExp.Arguments[2] as UnaryExpression)?.Operand as LambdaExpression;
                            var arg3 = (callExp.Arguments[3] as UnaryExpression)?.Operand as LambdaExpression;
                            var arg4 = (callExp.Arguments[4] as UnaryExpression)?.Operand as LambdaExpression;
                            FreeSqlExtensionsLinqSql.InternalJoin2(_select, arg2, arg3, arg4);
                            _select._selectExpression = arg4.Body;
                            break;
                        }
                        return throwCallExp($" 不支持 {callExp.Arguments.Count}个参数的方法");

                    case "SelectMany":
                        if (callExp.Arguments.Count == 3)
                        {
                            var arg1 = (callExp.Arguments[1] as UnaryExpression)?.Operand as LambdaExpression;
                            var arg2 = (callExp.Arguments[2] as UnaryExpression)?.Operand as LambdaExpression;
                            FreeSqlExtensionsLinqSql.InternalSelectMany2(_select, arg1, arg2);
                            _select._selectExpression = arg2.Body;
                            break;
                        }
                        return throwCallExp($" 不支持 {callExp.Arguments.Count}个参数的方法");

                    case "DefaultIfEmpty":
                        break;

                    case "Last":
                    case "LastOrDefault":
                        return throwCallExp(CoreErrorStrings.Not_Support);

                    case "GroupBy":
                        return throwCallExp(CoreErrorStrings.Not_Support);

                    default:
                        return throwCallExp(CoreErrorStrings.Not_Support);
                }
            }
            if (tresult == null) return null;
            if (isfirst)
            {
                _select.Limit(1);
                if (_select._selectExpression != null)
                    return _select.InternalToList<TCurrent>(_select._selectExpression).FirstOrDefault();
                return _select.ToList().FirstOrDefault();
            }
            if (_select._selectExpression != null)
                return _select.InternalToList<TCurrent>(_select._selectExpression);
            return _select.ToList();
        }
    }
}