EFCore使用JSON_VALUE查询json对象的值

Intro

SqlServer 从2016开始支持 JSON 操作，可以使用 JSON_VALUE 查询 JSON 对象的某个属性值，更多介绍，现在公司的一些项目主要是使用 EF Core，手写sql较少，针对比较简单的 JSON_VALUE 查询想通过 DbFunction 来实现，于是就有了这篇文章的探索。

定义 JSON_VALUE DbFunction

 ???public static class DbFunctions ???{ ???????[DbFunction("JSON_VALUE", "")] ???????public static string JsonValue(string column, [NotParameterized] string path) ???????{ ???????????throw new NotSupportedException(); ???????} ???}

在 DbContext 中注册 DbFunction

 ???public class TestDbContext : DbContext ???{ ???????public TestDbContext(DbContextOptions<TestDbContext> options) : base(options) ???????{ ???????} ???????public DbSet<TestEntity> TestEntities { get; set; } ???????protected override void OnModelCreating(ModelBuilder modelBuilder) ???????{ ???????????modelBuilder.HasDbFunction(() => DbFunctions.JsonValue(default(string), default(string))); ???????} ???} ???public class TestEntity ???{ ???????[Key] ???????[DatabaseGenerated(DatabaseGeneratedOption.Identity)] ???????public int Id { get; set; } ???????public string Extra { get; set; } ???????public DateTime CreatedAt { get; set; } ???}

使用注册的 DbFunction 查询 JSON_VALUE

数据库中添加了三条测试数据

var loggerFactory = new LoggerFactory();loggerFactory.AddLog4Net();var optionsBuilder = new DbContextOptionsBuilder<TestDbContext>() ???????????????.UseLoggerFactory(loggerFactory) ???????????????.UseSqlServer("server=.;database=Test;Integrated Security=True");var db = new TestDbContext(optionsBuilder.Options);var names = db.TestEntities.AsNoTracking().Select(t => DbFunctions.JsonValue(t.Extra, "$.Name")).ToArray();

监控生成的Sql语句

我这里通过 log4net 记录执行的 sql 语句，监控到执行的sql语句如下：

SELECT JSON_VALUE([t].[Extra], N'$.Name')FROM [TestEntities] AS [t]

Source

示例代码： https://github.com/WeihanLi/WeihanLi.EntityFramework/blob/master/samples/WeihanLi.EntityFramework.Samples/Program.cs

Reference

• https://docs.microsoft.com/en-us/sql/t-sql/functions/json-value-transact-sql?view=sql-server-2017
• https://docs.microsoft.com/en-us/sql/relational-databases/json/json-path-expressions-sql-server?view=sql-server-2017
• https://stackoverflow.com/questions/52017204/expression-tree-to-sql-with-ef-core
• https://docs.microsoft.com/en-us/ef/core/what-is-new/ef-core-2.0#database-scalar-function-mapping

EFCore使用JSON_VALUE查询json对象的值

原文地址：https://www.cnblogs.com/weihanli/p/use-json-value-in-ef-core.html