记一次使用dapper的坑（数据库与类映射）（转）

本来是测试dapper转换真正的mysql语句后是否能真正使用索引的，不过被一个地方卡住了，在查询的时候一直不能映射强类型的值。找了大概1小时才找到处理的方式，记录下来免得忘记。

先看表设计

 

image.png

类定义，因为程序如果使用下划线感觉会很突兀，不符合C#类命名规范，所以统一使用了大写开头的驼峰式命名，找了一个通过Attribute的映射到数据库字段的方式，代码在最后贴上

public class PersonInfo
    {
        [Column(Name = "mainid")]
        public long MainId { get; set; }

        [Column(Name = "id_card_number")]
        public string IdCardNumber { get; set; }

        [Column(Name = "name")]
        public string Name { get; set; }

        [Column(Name = "created_datetime")]
        public DateTime CreatedDateTime { get; set; }

    }

先插入数据，通过dapper插入数据是没啥问题的，看看数据

 

image.png

代码也是正常，即使不指定列，只要多传入一个MainId也是能正常插入数据的

static void Main(string[] args)
        {
            string connectionString = @"server=localhost;port=3306;database=tor_db_test;user=root;Password=123456;CharSet=utf8mb4;Pooling=true;Min Pool Size=0;Max Pool Size=100;";
            using (IDbConnection connection = new MySqlConnection(connectionString))
            {
                var resultInt = connection.Execute("INSERT INTO person_info VALUES (@MainId,@IdCardNumber,@Name,@CreatedDateTime)", new PersonInfo()
                {
                    MainId = 2,
                    IdCardNumber = "440684200001010000",
                    Name = "呜呜呜",
                    CreatedDateTime = DateTime.Now
                });
                Console.WriteLine(resultInt);
            }

            Console.WriteLine();
            Console.ReadLine();
        }

但是查询就有问题了

static void Main(string[] args)
        {
            string connectionString = @"server=localhost;port=3306;database=tor_db_test;user=root;Password=123456;CharSet=utf8mb4;Pooling=true;Min Pool Size=0;Max Pool Size=100;";
            using (IDbConnection connection = new MySqlConnection(connectionString))
            {
                //var p = connection.Query<PersonInfo>("SELECT * FROM person_info ");
                var p = connection.Query<PersonInfo>("SELECT mainid,id_card_number,name,created_datetime FROM person_info ");
                Console.WriteLine(JsonConvert.SerializeObject(p, Formatting.Indented));
            }

            Console.WriteLine();
            Console.ReadLine();
        }

查询结果如下，强类型查询无法自动匹配值了

 

image.png

试一下动态类型，正常的，所以问题定位在dapper强类型转换没能匹配上

 

image.png

最后发现有这个配置，主要是忽略下划线再进行匹配

Dapper.DefaultTypeMap.MatchNamesWithUnderscores = true;

加上之后就正常了

 

image.png

代码如下

static void Main(string[] args)
        {
            string connectionString = @"server=localhost;port=3306;database=tor_db_test;user=root;Password=123456;CharSet=utf8mb4;Pooling=true;Min Pool Size=0;Max Pool Size=100;";
            using (IDbConnection connection = new MySqlConnection(connectionString))
            {
                Dapper.DefaultTypeMap.MatchNamesWithUnderscores = true;
                var p = connection.Query<PersonInfo>("SELECT mainid,id_card_number,name,created_datetime FROM person_info ");
                Console.WriteLine(JsonConvert.SerializeObject(p, Formatting.Indented));
            }

            Console.WriteLine();
            Console.ReadLine();
        }

通过Attribute映射代码,网上找的，么得注释

/// <summary>
    /// Uses the Name value of the <see cref="ColumnAttribute"/> specified to determine
    /// the association between the name of the column in the query results and the member to
    /// which it will be extracted. If no column mapping is present all members are mapped as
    /// usual.
    /// </summary>
    /// <typeparam name="T">The type of the object that this association between the mapper applies to.</typeparam>
    public class ColumnAttributeTypeMapper<T> : FallbackTypeMapper
    {
        public ColumnAttributeTypeMapper()
            : base(new SqlMapper.ITypeMap[]
                {
                    new CustomPropertyTypeMap(
                       typeof(T),
                       (type, columnName) =>
                           type.GetProperties().FirstOrDefault(prop =>
                               prop.GetCustomAttributes(false)
                                   .OfType<ColumnAttribute>()
                                   .Any(attr => attr.Name == columnName)
                               )
                       ),
                    new DefaultTypeMap(typeof(T))
                })
        {
        }
    }

    [AttributeUsage(AttributeTargets.Property, AllowMultiple = true)]
    public class ColumnAttribute : Attribute
    {
        public string Name { get; set; }
    }
    public class FallbackTypeMapper : SqlMapper.ITypeMap
    {
        private readonly IEnumerable<SqlMapper.ITypeMap> _mappers;

        public FallbackTypeMapper(IEnumerable<SqlMapper.ITypeMap> mappers)
        {
            _mappers = mappers;
        }


        public ConstructorInfo FindConstructor(string[] names, Type[] types)
        {
            foreach (var mapper in _mappers)
            {
                try
                {
                    ConstructorInfo result = mapper.FindConstructor(names, types);
                    if (result != null)
                    {
                        return result;
                    }
                }
                catch (NotImplementedException)
                {
                }
            }
            return null;
        }

        public SqlMapper.IMemberMap GetConstructorParameter(ConstructorInfo constructor, string columnName)
        {
            foreach (var mapper in _mappers)
            {
                try
                {
                    var result = mapper.GetConstructorParameter(constructor, columnName);
                    if (result != null)
                    {
                        return result;
                    }
                }
                catch (NotImplementedException)
                {
                }
            }
            return null;
        }

        public SqlMapper.IMemberMap GetMember(string columnName)
        {
            foreach (var mapper in _mappers)
            {
                try
                {
                    var result = mapper.GetMember(columnName);
                    if (result != null)
                    {
                        return result;
                    }
                }
                catch (NotImplementedException)
                {
                }
            }
            return null;
        }


        public ConstructorInfo FindExplicitConstructor()
        {
            return _mappers
                .Select(mapper => mapper.FindExplicitConstructor())
                .FirstOrDefault(result => result != null);
        }
    }

完

 

 

链接：https://www.jianshu.com/p/ea588d837014