using System;
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using System.ComponentModel;
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using System.Linq.Expressions;
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using System.Reflection;
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namespace CmsQueryExtensions.Extension
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{
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public class WhereHelper<T>
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//where T : class
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{
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public ParameterExpression param;
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public BinaryExpression filter;
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private MemberExpression common_left;
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private UnaryExpression common_right;
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//private ConstantExpression common_right;
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public WhereHelper()
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{
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param = Expression.Parameter(typeof(T), "c");//构建 c=> 结构
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//1==1
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Expression left = Expression.Constant(1);
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filter = Expression.Equal(left, left);//构建出 c=> 1=1
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}
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public Expression<Func<T, bool>> GetExpression()
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{
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return Expression.Lambda<Func<T, bool>>(filter, param);
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}
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private void CommonLeftRight(string propertyName, object value)
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{
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common_left = Expression.Property(param, typeof(T).GetProperty(propertyName));//构建构建c.{propertyName}的结构
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var member = Expression.Property(param, propertyName);
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var propertyType = ((PropertyInfo)member.Member).PropertyType;
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var converter = TypeDescriptor.GetConverter(propertyType); // 1
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if (!converter.CanConvertFrom(typeof(string))) // 2
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throw new NotSupportedException();
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var propertyValue = converter.ConvertFromInvariantString(value.ToString()); // 3
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var constant = Expression.Constant(propertyValue);
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//common_right = constant; // 4
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common_right = Expression.Convert(constant, propertyType); // 4 //这里必须转换，否则如果字段可为NULL，就会报错
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// common_right = Expression.Constant(value, value.GetType());//构建一个常量,值是 value
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}
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/// <summary>
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/// 等于 =
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/// </summary>
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/// <param name="propertyName"></param>
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/// <param name="value"></param>
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public void Equal(string propertyName, object value)
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{
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CommonLeftRight(propertyName, value);
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Expression result = Expression.Equal(common_left, common_right);
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filter = Expression.AndAlso(filter, result);
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}
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/// <summary>
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/// 不等于 <>
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/// </summary>
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/// <param name="propertyName"></param>
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/// <param name="value"></param>
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public void NotEqual(string propertyName, object value)
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{
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CommonLeftRight(propertyName, value);
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Expression result = Expression.NotEqual(common_left, common_right);
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filter = Expression.AndAlso(filter, result);
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}
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/// <summary>
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/// 大于 >
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/// </summary>
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/// <param name="propertyName"></param>
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/// <param name="value"></param>
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public void GreaterThan(string propertyName, object value)
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{
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CommonLeftRight(propertyName, value);
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Expression result = Expression.GreaterThan(common_left, common_right);
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filter = Expression.AndAlso(filter, result);
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}
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/// <summary>
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/// 大于等于 >=
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/// </summary>
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/// <param name="propertyName"></param>
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/// <param name="value"></param>
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public void GreaterThanOrEqual(string propertyName, object value)
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{
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CommonLeftRight(propertyName, value);
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Expression result = Expression.GreaterThanOrEqual(common_left, common_right);
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filter = Expression.AndAlso(filter, result);
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}
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/// <summary>
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/// 小于 <
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/// </summary>
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/// <param name="propertyName"></param>
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/// <param name="value"></param>
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public void LessThan(string propertyName, object value)
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{
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CommonLeftRight(propertyName, value);
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Expression result = Expression.LessThan(common_left, common_right);
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filter = Expression.AndAlso(filter, result);
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}
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/// <summary>
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/// 小于等于 <=
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/// </summary>
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/// <param name="propertyName"></param>
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/// <param name="value"></param>
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public void LessThanOrEqual(string propertyName, object value)
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{
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CommonLeftRight(propertyName, value);
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Expression result = Expression.LessThanOrEqual(common_left, common_right);
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filter = Expression.AndAlso(filter, result);
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}
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/// <summary>
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/// 包含 LIKE
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/// </summary>
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/// <param name="propertyName"></param>
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/// <param name="value"></param>
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public void Contains(string propertyName, string value)
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{
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Expression left = Expression.Property(param, typeof(T).GetProperty(propertyName));
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Expression right = Expression.Constant(value, value.GetType());
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Expression result = Expression.Call(left, typeof(string).GetMethod("Contains", new Type[] { typeof(string) }), right);
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filter = Expression.AndAlso(filter, result);
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}
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}
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}
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