如何在方法内执行 LINQ where 子句

Question

我想在方法中执行 LINQ where 子句。

例如：

using (BP_TTOKEntities db = new BP_TTOKEntities(_dto.IdTenant))
{
    var res = db.doc003fornitura

    if (fornitura.Numero != null) //Filtro numero
    {
        if (!fornitura.Numero.LBoundIsNull) res = res.Where(x => x.fornitura_nro >= fornitura.Numero.LBound);
        if (!fornitura.Numero.UBoundIsNull) res = res.Where(x => x.fornitura_nro <= fornitura.Numero.UBound);
    }
}

我会替换：

if (!fornitura.Numero.LBoundIsNull) res = res.Where(x => x.fornitura_nro >= fornitura.Numero.LBound);
if (!fornitura.Numero.UBoundIsNull) res = res.Where(x => x.fornitura_nro <= fornitura.Numero.UBound);

像这样：

res = fornitura.Numero.Where<doc003fornitura>(x.fornitura_nro);

可能吗？我该如何制作方法？

谢谢路易吉。

Answer 1

我是这样解决的

这是调用：

if (fornitura.Numero != null) res = fornitura.Numero.Compare(res, x => x.fornitura_nro);

这些是class的方法：

            public IQueryable<TEntity> Compare<TEntity>(IQueryable<TEntity> source, Expression<Func<TEntity, Nullable<short>>> func)
            {
                return _Compare(source, func);
            }

            public IQueryable<TEntity> Compare<TEntity>(IQueryable<TEntity> source, Expression<Func<TEntity, Nullable<int>>> func)
            {
                return _Compare(source, func);
            }

            public IQueryable<TEntity> Compare<TEntity>(IQueryable<TEntity> source, Expression<Func<TEntity, Nullable<DateTime>>> func)
            {
                return _Compare(source, func);
            }

            public IQueryable<TEntity> Compare<TEntity>(IQueryable<TEntity> source, Expression<Func<TEntity, string>> func)
            {
                return _Compare(source, func);
            }

            private IQueryable<TEntity> _Compare<TEntity>(IQueryable<TEntity> source, object func)
            {
                IQueryable<TEntity> res = source;

                Type type = func.GetType();
                Expression funcBody = (Expression)type.GetProperty("Body").GetValue(func);
                IEnumerable<ParameterExpression> funcParameters = (IEnumerable<ParameterExpression>)type.GetProperty("Parameters").GetValue(func);

                if (!this.LBoundIsNull)
                {
                    Expression ge = _Comparison(funcBody, Expression.Constant(_lBound), ExpressionType.GreaterThanOrEqual);
                    var lambda = Expression.Lambda<Func<TEntity, bool>>(ge, funcParameters);
                    res = res.Where(lambda);
                }

                if (!this.UBoundIsNull)
                {
                    Expression le = _Comparison(funcBody, Expression.Constant(_uBound), ExpressionType.LessThanOrEqual);
                    var lambda = Expression.Lambda<Func<TEntity, bool>>(le, funcParameters);
                    res = res.Where(lambda);
                }

                return res;
            }

            private Expression _Comparison(Expression left, Expression right, ExpressionType expressionType)
            {
                if (left.Type.IsNullable() && !right.Type.IsNullable())
                    right = Expression.Convert(right, left.Type);
                else if (!left.Type.IsNullable() && right.Type.IsNullable())
                    left = Expression.Convert(left, right.Type);

                if (left.Type == typeof(string))
                {
                    var method = left.Type.GetMethod("CompareTo", new[] { typeof(string) });
                    var result = Expression.Call(left, method, right);
                    return Expression.MakeBinary(expressionType, result, Expression.Constant(0));
                }
                else
                    switch (expressionType)
                    {
                        case ExpressionType.GreaterThanOrEqual:
                            return Expression.GreaterThanOrEqual(left, right);
                        case ExpressionType.LessThanOrEqual:
                            return Expression.LessThanOrEqual(left, right);
                        default:
                            return Expression.Equal(left, right);
                    }
            }

谢谢！

如何在方法内执行 LINQ where 子句

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