如何获取OData Queryable Web API端点过滤器并从DTO对象映射它? [英] How to take OData Queryable Web API endpoint filter and map it from DTO object?
问题描述
我有一个简单的Web API端点，可以接受传入的OData查询:
I have a simple Web API endpoint which can accept incoming OData queries:
public IActionResult GetProducts(ODataQueryOptions<ProductDTO> options)
{
var results = DomainLayer.GetProducts(options);
return Ok(results);
}
我特别希望能够针对 ProductDTO 对象进行查询，并能够针对DTO表示形式的属性进行过滤或排序.
I specifically want to be able to query against ProductDTO objects and to be able to filter or sort against the properties of the DTO representation.
我的设计问题是我想利用OData库的过滤器解析/应用逻辑，但又不想将数据库绑定的 ProductEntity 对象公开给Web API AND 我不想从我的 DataAccessLayer 中返回一个 IQueryable ，而仅返回 IEnumerable .
My design issue is that I want to take advantage of the filter parsing/applying logic of the OData library but I don't want to expose my database-bound ProductEntity objects to my Web API AND I do not want to return an IQueryable from my DataAccessLayer, only IEnumerables.
然后我要做的是从传入的 ODataQueryOptions 的 FilterQueryOption 属性中提取 Expression ，以便可以使用AutoMapper的Expression映射功能可将表达式从 Expression< Func< ProductDTO，bool> 映射到 Expression< Func< Product，bool> ，然后最终映射到 Expression< Func< ProductEntity，bool>>> ，然后将其传递到我的 Table< ProductEntity> 上的 .Where()调用中>在哪里(希望)将过滤器应用到我的SQL数据库中(通过Linq-2-SQL)，然后我将其完全转换回DTO对象.
What I am trying to do then is to extract the Expression from the FilterQueryOption property of the incoming ODataQueryOptions so I can use AutoMapper's Expression Mapping feature to map the expression from a Expression<Func<ProductDTO, bool>> to a Expression<Func<Product, bool>> then finally to a Expression<Func<ProductEntity, bool>> where I will then pass it into a .Where() call on my Table<ProductEntity> where (hopefully) the filter is applied in my SQL database (via Linq-2-SQL) and then I just convert it all the way back to a DTO object after.
我遇到的最大问题是 queryable.Expression 返回的是 MethodCallExpression ，而不是 Expression< Func< ProductDTO，bool>> 就像我期望的那样，这意味着我无法像我计划的那样使用AutoMapper映射表达式...
The big showstopper I came across is that queryable.Expression is returning a MethodCallExpression rather than a Expression<Func<ProductDTO, bool>> like I expected, which means I can't map the expression with AutoMapper like I had planned...
我该如何解决?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using Microsoft.AspNet.OData.Query;
using AutoMapper.Extensions.ExpressionMapping;
using AutoMapper.QueryableExtensions;
namespace ProductApp
{
public class DomainLayer
{
public IEnumerable<ProductDTO> GetProductsByEntityOptions(ODataQueryOptions<ProductDTO> options)
{
var mapper = MyMapper.GetMapper();
// This is the trick to get the expression out of the FilterQueryOption...
IQueryable queryable = Enumerable.Empty<ProductDTO>().AsQueryable();
queryable = options.Filter.ApplyTo(queryable, new ODataQuerySettings());
var exp = (MethodCallExpression) queryable.Expression; // <-- This comes back as a MethodCallExpression...
// Map the expression to my intermediate Product object type
var mappedExp = mapper.Map<Expression<Func<Product, bool>>>(exp); // <-- But I want it as a Expression<Func<ProductDTO, bool>> so I can map it...
IEnumerable<Product> results = _dataAccessLayer.GetProducts(mappedExp);
return mapper.Map<IEnumerable<ProductDTO>>(results);
}
}
public class DataAccessLayer
{
public IEnumerable<Product> GetProducts(Expression<Func<Product, bool>> exp)
{
var mapper = MyMapper.GetMapper();
var mappedExp = mapper.Map<Expression<Func<ProductEntity, bool>>>(exp);
IEnumerable<ProductEntity> result = _dataContext.GetTable<ProductEntity>().Where(mappedExpression).ToList();
return mapper.Map<IEnumerable<Product>>(result);
}
}
}
参考:
- 在哪里找到了使表达式脱离过滤器的窍门: https://stackoverflow.com/a/16447514/1504964
- 一个相关的GitHub问题: https://github.com/OData/WebApi/issues/33
推荐答案
请注意，表达式包含的内容更像是 Notice that the expression contains looks more like this, 您得到的 The 因此，您所需要做的就是使用以下内容提取lambda表达式: So all you need is to extract the lambda expression with something like this: 并像这样使用它: 这篇关于如何获取OData Queryable Web API端点过滤器并从DTO对象映射它?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！ SOTests.Customer [].Where($ it => conditional-expression).因此，您可能必须从lambda中提取该条件表达式.
SOTests.Customer[].Where($it => conditional-expression). So, you might have to extract that conditional expression from the lambda. MethodCallExpression 就是-对" Queryable.Where< ProductDTO> "和lambda表达式 Expression< Func< ProductDTO的调用"，bool>> 是第二个参数(请记住 Queryable.Where 是 static 扩展方法，因此第一个参数表示 IQueryable< ProductDTO> )，并用MethodCallExpression you are getting is exactly that - a "call" to Queryable.Where<ProductDTO>, and the lambda expression Expression<Func<ProductDTO, bool>> you need is the second argument (remember the Queryable.Where is a static extension method, so the first argument is representing the IQueryable<ProductDTO>), wrapped with Expression.Quote. public static class ODataQueryOptionsExtensions
{
public static Expression<Func<T, bool>> GetFilter<T>(this ODataQueryOptions<T> options)
{
// The same trick as in the linked post
IQueryable query = Enumerable.Empty<T>().AsQueryable();
query = options.Filter.ApplyTo(query, new ODataQuerySettings());
// Extract the predicate from `Queryable.Where` call
var call = query.Expression as MethodCallExpression;
if (call != null && call.Method.Name == nameof(Queryable.Where) && call.Method.DeclaringType == typeof(Queryable))
{
var predicate = ((UnaryExpression)call.Arguments[1]).Operand;
return (Expression<Func<T, bool>>)predicate;
}
return null;
}
}
public class DomainLayer
{
public IEnumerable<ProductDTO> GetProductsByEntityOptions(ODataQueryOptions<ProductDTO> options)
{
var filter = options.GetFilter();
// Here the type of filter variable is Expression<Func<ProductDTO, bool>> as desired
// The rest ...
}
}
