StaffPerformance/wispro.sp.utility/Linq.Easy.cs

using System;
using System.Collections.ObjectModel;
using System.Linq.Expressions;
using System.Reflection;

namespace wispro.sp.utility
{
    public class Query
    {
        public enum Operators
        {
            None = 0,
            Equal = 1,
            GreaterThan = 2,
            GreaterThanOrEqual = 3,
            LessThan = 4,
            LessThanOrEqual = 5,
            Contains = 6,
            StartWith = 7,
            EndWidth = 8,
            Range = 9
        }
        public enum Condition
        {
            OrElse = 1,
            AndAlso = 2
        }
        public string Name { get; set; }
        public Operators Operator { get; set; }
        public object Value { get; set; }
        public object ValueMin { get; set; }
        public object ValueMax { get; set; }

        public class QueryCollection : Collection<Query>
        {
            public Expression<Func<T, bool>> AsExpression<T>(Query.Condition? condition = Query.Condition.OrElse) where T : class
            {
                Type targetType = typeof(T);
                TypeInfo typeInfo = targetType.GetTypeInfo();
                var parameter = Expression.Parameter(targetType, "m");
                Expression expression = null;
                Func<Expression, Expression, Expression> Append = (exp1, exp2) =>
                {
                    if (exp1 == null)
                    {
                        return exp2;
                    }
                    return (condition ?? Query.Condition.OrElse) == Query.Condition.OrElse ? Expression.OrElse(exp1, exp2) : Expression.AndAlso(exp1, exp2);
                };
                foreach (var item in this)
                {
                    var property = typeInfo.GetProperty(item.Name);
                    if (property == null ||
                        !property.CanRead ||
                        (item.Operator != Query.Operators.Range && item.Value == null) ||
                        (item.Operator == Query.Operators.Range && item.ValueMin == null && item.ValueMax == null))
                    {
                        continue;
                    }
                    Type realType = Nullable.GetUnderlyingType(property.PropertyType) ?? property.PropertyType;
                    if (item.Value != null)
                    {
                        item.Value = Convert.ChangeType(item.Value, realType);
                    }
                    Expression<Func<object>> valueLamba = () => item.Value;
                    switch (item.Operator)
                    {
                        case Query.Operators.Equal:
                            {
                                expression = Append(expression, Expression.Equal(Expression.Property(parameter, item.Name),
                                    Expression.Convert(valueLamba.Body, property.PropertyType)));
                                break;
                            }
                        case Query.Operators.GreaterThan:
                            {
                                expression = Append(expression, Expression.GreaterThan(Expression.Property(parameter, item.Name),
                                    Expression.Convert(valueLamba.Body, property.PropertyType)));
                                break;
                            }
                        case Query.Operators.GreaterThanOrEqual:
                            {
                                expression = Append(expression, Expression.GreaterThanOrEqual(Expression.Property(parameter, item.Name),
                                    Expression.Convert(valueLamba.Body, property.PropertyType)));
                                break;
                            }
                        case Query.Operators.LessThan:
                            {
                                expression = Append(expression, Expression.LessThan(Expression.Property(parameter, item.Name),
                                    Expression.Convert(valueLamba.Body, property.PropertyType)));
                                break;
                            }
                        case Query.Operators.LessThanOrEqual:
                            {
                                expression = Append(expression, Expression.LessThanOrEqual(Expression.Property(parameter, item.Name),
                                    Expression.Convert(valueLamba.Body, property.PropertyType)));
                                break;
                            }
                        case Query.Operators.Contains:
                            {
                                var nullCheck = Expression.Not(Expression.Call(typeof(string), "IsNullOrEmpty", null, Expression.Property(parameter, item.Name)));
                                var contains = Expression.Call(Expression.Property(parameter, item.Name), "Contains", null,
                                    Expression.Convert(valueLamba.Body, property.PropertyType));
                                expression = Append(expression, Expression.AndAlso(nullCheck, contains));
                                break;
                            }
                        case Query.Operators.StartWith:
                            {
                                var nullCheck = Expression.Not(Expression.Call(typeof(string), "IsNullOrEmpty", null, Expression.Property(parameter, item.Name)));
                                var startsWith = Expression.Call(Expression.Property(parameter, item.Name), "StartsWith", null,
                                    Expression.Convert(valueLamba.Body, property.PropertyType));
                                expression = Append(expression, Expression.AndAlso(nullCheck, startsWith));
                                break;
                            }
                        case Query.Operators.EndWidth:
                            {
                                var nullCheck = Expression.Not(Expression.Call(typeof(string), "IsNullOrEmpty", null, Expression.Property(parameter, item.Name)));
                                var endsWith = Expression.Call(Expression.Property(parameter, item.Name), "EndsWith", null,
                                    Expression.Convert(valueLamba.Body, property.PropertyType));
                                expression = Append(expression, Expression.AndAlso(nullCheck, endsWith));
                                break;
                            }
                        case Query.Operators.Range:
                            {
                                Expression minExp = null, maxExp = null;
                                if (item.ValueMin != null)
                                {
                                    var minValue = Convert.ChangeType(item.ValueMin, realType);
                                    Expression<Func<object>> minValueLamda = () => minValue;
                                    minExp = Expression.GreaterThanOrEqual(Expression.Property(parameter, item.Name), Expression.Convert(minValueLamda.Body, property.PropertyType));
                                }
                                if (item.ValueMax != null)
                                {
                                    var maxValue = Convert.ChangeType(item.ValueMax, realType);
                                    Expression<Func<object>> maxValueLamda = () => maxValue;
                                    maxExp = Expression.LessThanOrEqual(Expression.Property(parameter, item.Name), Expression.Convert(maxValueLamda.Body, property.PropertyType));
                                }

                                if (minExp != null && maxExp != null)
                                {
                                    expression = Append(expression, Expression.AndAlso(minExp, maxExp));
                                }
                                else if (minExp != null)
                                {
                                    expression = Append(expression, minExp);
                                }
                                else if (maxExp != null)
                                {
                                    expression = Append(expression, maxExp);
                                }

                                break;
                            }
                    }
                }
                if (expression == null)
                {
                    return null;
                }
                return ((Expression<Func<T, bool>>)Expression.Lambda(expression, parameter));
            }
        }
    }
}