使用实体框架创建动态查询

问题描述

我想知道使用实体框架和 linq 创建动态查询的最佳方式是什么.

I would like to know what is the best way of creating dynamic queries with entity framework and linq.

我想创建一个服务，该服务具有许多用于排序和过滤的参数(超过 50 个).我将从 gui 获取对象，这些对象将在其中填写...并且查询将从单个服务方法执行.

I want to create a service that has many parameters for sorting and filtering (over 50). I will be getting object from gui where these will be filled out... and query will be executed from a single service method.

我环顾四周，发现我可以动态创建一个字符串，该字符串可以在我的方法结束时执行.我非常不喜欢这种方式.有一个更好的方法吗?最好使用编译检查类型安全?

I looked around And I saw that I could dynamically create a string that can be executed at the end of my method. I don't like this way very much. Is there a better way to do this? Preferably type safe with compile check?

推荐答案

您可以逐步编写一个 IQueryable.假设你有一个 FilterDefinition 类，它描述了用户想要如何过滤......

You could compose an IQueryable<T> step by step. Assuming you have a FilterDefinition class which describes how the user wants to filter ...

public class FilterDefinition
{
    public bool FilterByName { get; set; }
    public string NameFrom { get; set; }
    public string NameTo { get; set; }

    public bool FilterByQuantity { get; set; }
    public double QuantityFrom { get; set; }
    public double QuantityTo { get; set; }
}

...然后你可以像这样构建一个查询:

... then you could build a query like so:

public IQueryable<SomeEntity> GetQuery(FilterDefinition filter)
{
    IQueryable<SomeEntity> query = context.Set<SomeEntity>();
    // assuming that you return all records when nothing is specified in the filter

    if (filter.FilterByName)
        query = query.Where(t =>
            t.Name >= filter.NameFrom && t.Name <= filter.NameTo);

    if (filter.FilterByQuantity)
        query = query.Where(t =>
            t.Quantity >= filter.QuantityFrom && t.Quantity <= filter.QuantityTo);

    return query;
}

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