ORM FreeSql之Expression表达式拼接参数扩展
在FreeSql源码中Expression表达式拼接默认最多支持到5个泛型参数,当我们使用表关联比较多的时候,就需要进行扩展。
新建一个类,将命名空间改为System.Linq.Expressions,并加入参数扩展
namespace System.Linq.Expressions
{
static partial class LambadaExpressionExtensions
{
//如需扩展增加泛型参数即可
#region T1, T2, T3, T4, T5 ,T6
/// <summary>
/// 使用 and 拼接两个 lambda 表达式
/// </summary>
/// <returns></returns>
public static Expression<Func<T1, T2, T3, T4, T5, T6, bool>> And<T1, T2, T3, T4, T5, T6>(this Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp1, Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp2) => And(exp1, true, exp2);
/// <summary>
/// 使用 and 拼接两个 lambda 表达式
/// </summary>
/// <param name="exp1"></param>
/// <param name="condition">true 时生效</param>
/// <param name="exp2"></param>
/// <returns></returns>
public static Expression<Func<T1, T2, T3, T4, T5, T6, bool>> And<T1, T2, T3, T4, T5, T6>(this Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp1, bool condition, Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp2) => (Expression<Func<T1, T2, T3, T4, T5, T6, bool>>)InternalAndOrExpression(condition, exp1, exp2, true);
/// <summary>
/// 使用 or 拼接两个 lambda 表达式
/// </summary>
/// <returns></returns>
public static Expression<Func<T1, T2, T3, T4, T5, T6, bool>> Or<T1, T2, T3, T4, T5, T6>(this Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp1, Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp2) => Or(exp1, true, exp2);
/// <summary>
/// 使用 or 拼接两个 lambda 表达式
/// </summary>
/// <param name="exp1"></param>
/// <param name="condition">true 时生效</param>
/// <param name="exp2"></param>
/// <returns></returns>
public static Expression<Func<T1, T2, T3, T4, T5, T6, bool>> Or<T1, T2, T3, T4, T5, T6>(this Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp1, bool condition, Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp2) => (Expression<Func<T1, T2, T3, T4, T5, T6, bool>>)InternalAndOrExpression(condition, exp1, exp2, false);
/// <summary>
/// 将 lambda 表达式取反
/// </summary>
/// <param name="exp"></param>
/// <param name="condition">true 时生效</param>
/// <returns></returns>
public static Expression<Func<T1, T2, T3, T4, T5, T6, bool>> Not<T1, T2, T3, T4, T5, T6>(this Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp, bool condition = true) => (Expression<Func<T1, T2, T3, T4, T5, T6, bool>>)InternalNotExpression(condition, exp);
#endregion
#region 通用表达式方法
static LambdaExpression InternalAndOrExpression(bool condition, LambdaExpression exp1, LambdaExpression exp2, bool isAndAlso)
{
if (condition == false) return exp1;
if (exp1 == null) return exp2;
if (exp2 == null) return exp1;
var newParameters = exp1.Parameters.Select((a, b) => Expression.Parameter(a.Type, a.Name /*$"new{b}"*/)).ToArray();
var left = new NewExpressionVisitor(newParameters, exp1.Parameters.ToArray()).Replace(exp1.Body);
var right = new NewExpressionVisitor(newParameters, exp2.Parameters.ToArray()).Replace(exp2.Body);
var body = isAndAlso ? Expression.AndAlso(left, right) : Expression.OrElse(left, right);
return Expression.Lambda(exp1.Type, body, newParameters);
}
static LambdaExpression InternalNotExpression(bool condition, LambdaExpression exp)
{
if (condition == false) return exp;
if (exp == null) return null;
var newParameters = exp.Parameters.Select((a, b) => Expression.Parameter(a.Type, a.Name /*$"new{b}"*/)).ToArray();
var body = Expression.Not(exp.Body);
return Expression.Lambda(exp.Type, body, newParameters);
}
internal class NewExpressionVisitor : ExpressionVisitor
{
ParameterExpression[] _newParameters;
ParameterExpression[] _oldParameters;
public NewExpressionVisitor(ParameterExpression newParam, ParameterExpression oldParam) : this(new[] { newParam }, new[] { oldParam }) { }
public NewExpressionVisitor(ParameterExpression[] newParams, ParameterExpression[] oldParams)
{
this._newParameters = newParams;
this._oldParameters = oldParams;
}
public Expression Replace(Expression exp) => this.Visit(exp);
protected override Expression VisitParameter(ParameterExpression node)
{
for (var a = 0; a < _oldParameters.Length; a++)
if (_oldParameters[a] == node)
return _newParameters[a];
return node;
}
}
#endregion
}
}
以上代码是将表达式拼接扩展至6个泛型参数,以此类推。
因为属于同一个命名空间,可以直接使用。