Dapper中数据表的字段(列)与实体属性不一致时，如何手动配置它们之间的映射？...

NET[C#]Dapper中数据表的字段(列)与实体属性不一致时，如何手动配置它们之间的映射？

问题描述

比如有如下的数据表结构：
Person:

person_id  int
first_name varchar(50) last_name varchar(50) 

以及实体类：
Person:

public class Person 
{
    public int PersonId { get; set; } public string FirstName { get; set; } public string LastName { get; set; } } 

在C#程序中，使用Dapper做查询时，如何配置数据表字段(列)和实体类属性之间的映射呢？

方案一

var sql = @"select top 1 person_id PersonId, first_name FirstName, last_name LastName from Person";
using (var conn = ConnectionFactory.GetConnection())
{
    var person = conn.Query(sql).ToList(); return person; } 

方案二

使用 ColumnAttribute 属性
完整的代码片段：

namespace YourNamespace
{
    /// 

    /// Uses the Name value of the  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. /// 
 /// The type of the object that this association between the mapper applies to. public class ColumnAttributeTypeMapper : FallbackTypeMapper { public ColumnAttributeTypeMapper() : base(new SqlMapper.ITypeMap[] { new CustomPropertyTypeMap( typeof(T), (type, columnName) => type.GetProperties().FirstOrDefault(prop => prop.GetCustomAttributes(false) .OfType() .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 _mappers; public FallbackTypeMapper(IEnumerable 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); } } } 

调用方法：

public class Person 
{
     [Column(Name="person_id")]
    public int PersonId { get; set; } [Column(Name="first_name")] public string FirstName { get; set; } [Column(Name="last_name")] public string LastName { get; set; } } 

方案三

使用 CustomPropertyTypeMap 自定义属性类型映射类，如：

public class ColumnMap
{
    private readonly Dictionary<string, string> forward = new Dictionary<string, string>(); private readonly Dictionary<string, string> reverse = new Dictionary<string, string>(); public void Add(string t1, string t2) { forward.Add(t1, t2); reverse.Add(t2, t1); } public string this[string index] { get { // Check for a custom column map. if (forward.ContainsKey(index)) return forward[index]; if (reverse.ContainsKey(index)) return reverse[index]; // If no custom mapping exists, return the value passed in. return index; } } } 

配置列映射关系

var columnMap = new ColumnMap();
columnMap.Add("Field1", "Column1");
columnMap.Add("Field2", "Column2"); columnMap.Add("Field3", "Column3"); SqlMapper.SetTypeMap(typeof (MyClass), new CustomPropertyTypeMap(typeof (MyClass), (type, columnName) => type.GetProperty(columnMap[columnName]))); 

方案四

查询时使用LINQ

 var sql = @"select top 1 person_id, first_name, last_name from Person";
    using (var conn = ConnectionFactory.GetConnection())
    {
        List person = conn.Query(sql) .Select(item => new Person() { PersonId = item.person_id, FirstName = item.first_name, LastName = item.last_name } .ToList(); return person; } 

http://2sharings.com/2018/dapper-orm-manually-map-column-names-with-class-properties-in-csharp-application

转载于:https://www.cnblogs.com/efreer/p/8277329.html