如何映射表达式< Func< TEntity，bool>>>到表达< Func< TDbEntity，bool>>> [英] How to map Expression<Func<TEntity, bool>> to Expression<Func<TDbEntity, bool>>

问题描述

如何映射

：表达式< Func< TEntity，bool>>
到：表达< Func< TDbEntity，bool>>

where TEntity: class, new() and TDbEntity: class, new()

TEntity来自Domain和TDbEntity来自于基础架构层，但具有相同的属性。

TEntity is from Domain and TDbEntity is from Infrastructure layer, but have same properties.

可以吗？

推荐答案

对于相对简单的情况（我猜你的表达式很简单）可以使用 ExpressionVisitor ，只需要几个覆盖。例如：

For relatively simple cases (and I guess in your case expressions are simple) you can use ExpressionVisitor with only a couple of overrides. For example:

public static class ExpressionExtensions {
    public static Expression<Func<TTo, bool>> ReplaceParameter<TFrom, TTo>(this Expression<Func<TFrom, bool>> target) {
        return (Expression<Func<TTo, bool>>) new WhereReplacerVisitor<TFrom, TTo>().Visit(target);
    }
    private class WhereReplacerVisitor<TFrom, TTo> : ExpressionVisitor {
        private readonly ParameterExpression _parameter = Expression.Parameter(typeof(TTo), "c");

        protected override Expression VisitLambda<T>(Expression<T> node) {
            // replace parameter here
            return Expression.Lambda(Visit(node.Body), _parameter);
        }            

        protected override Expression VisitMember(MemberExpression node) {
            // replace parameter member access with new type
            if (node.Member.DeclaringType == typeof(TFrom) && node.Expression is ParameterExpression) {
                return Expression.PropertyOrField(_parameter, node.Member.Name);
            }
            return base.VisitMember(node);
        }
    }
}

用法是：

Expression<Func<ErrorModel, bool>> where = (c) => c.Created <= DateTime.UtcNow && c.ErrorCode == "code";
var replaced = where.ReplaceParameter<ErrorModel, Error>();

这篇关于如何映射表达式< Func< TEntity，bool>>>到表达< Func< TDbEntity，bool>>>的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！