关于Dapper的使用笔记3

时间:2022-12-26 09:45:14

1、默认的类型映射,直接以实体属性(或字段)映射到SQL中字段,(名称可以忽略大小写)

2、如果字段带下划线的,设置Dapper.DefaultTypeMap.MatchNamesWithUnderscores = true; 即可。

3、正因为有这个DefaultTypeMap默认的映射策略,所以,一般情况下,可以直接通过SQL查询,生成实体List.

4、Dapper还是以数据库为中心的思考问题模式,不同于Entity framework和nhibernate,提倡以实体到DB的思考问题方式。

5、Dapper在处理实体关联方面算是硬伤了,只能程序员自已根据DTO的模型去自已动手组装了。

附上代码

    /// <summary>
/// 表示Dapper默认的类型映射策略
/// Represents default type mapping strategy used by Dapper
/// </summary>
sealed partial class DefaultTypeMap : SqlMapper.ITypeMap
{
/// <summary>
/// 要映射的实体,所有的字段
/// </summary>
private readonly List<FieldInfo> _fields;

/// <summary>
/// 要映射的实体,所有的属性
/// </summary>
private readonly List<PropertyInfo> _properties;

/// <summary>
/// 要映射的实体类型
/// </summary>
private readonly Type _type;

/// <summary>
/// 构造函数,创建缺省的类型映射策略
/// Creates default type map
/// </summary>
/// <param name="type">Entity type</param>
public DefaultTypeMap(Type type)
{
if (type == null)
throw new ArgumentNullException("type");

_fields
= GetSettableFields(type);
_properties
= GetSettableProps(type);
_type
= type;
}

/// <summary>
/// 获取属性的setter访问器
/// </summary>
/// <param name="propertyInfo"></param>
/// <param name="type"></param>
/// <returns></returns>
internal static MethodInfo GetPropertySetter(PropertyInfo propertyInfo, Type type)
{
return propertyInfo.DeclaringType == type ?
propertyInfo.GetSetMethod(
true) :
propertyInfo.DeclaringType.GetProperty(
propertyInfo.Name,
BindingFlags.Public
| BindingFlags.NonPublic | BindingFlags.Instance,
Type.DefaultBinder,
propertyInfo.PropertyType,
propertyInfo.GetIndexParameters().Select(p
=> p.ParameterType).ToArray(),
null).GetSetMethod(true);
}

/// <summary>
/// 获取某类型所有可写(有set,包括私有)的成员属性
/// </summary>
/// <param name="t"></param>
/// <returns></returns>
internal static List<PropertyInfo> GetSettableProps(Type t)
{
return t
.GetProperties(BindingFlags.Public
| BindingFlags.NonPublic | BindingFlags.Instance)
.Where(p
=> GetPropertySetter(p, t) != null)
.ToList();
}

/// <summary>
/// 获取某类型所有的成员字段
/// </summary>
/// <param name="t"></param>
/// <returns></returns>
internal static List<FieldInfo> GetSettableFields(Type t)
{
return t.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance).ToList();
}

/// <summary>
/// 获取最佳的成员构造器,优先顺序:public的构造器0, 其它构造器1, private的构造器2,然后再按参数匹配
/// Finds best constructor
/// </summary>
/// <param name="names">DataReader column names</param>
/// <param name="types">DataReader column types</param>
/// <returns>Matching constructor or default one</returns>
public ConstructorInfo FindConstructor(string[] names, Type[] types)
{
var constructors = _type.GetConstructors(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
foreach (ConstructorInfo ctor in constructors.OrderBy(c => c.IsPublic ? 0 : (c.IsPrivate ? 2 : 1)).ThenBy(c => c.GetParameters().Length))
{
ParameterInfo[] ctorParameters
= ctor.GetParameters();
if (ctorParameters.Length == 0)
return ctor;

if (ctorParameters.Length != types.Length)
continue;

int i = 0;
for (; i < ctorParameters.Length; i++)
{
if (!String.Equals(ctorParameters[i].Name, names[i], StringComparison.OrdinalIgnoreCase))
break;
if (types[i] == typeof(byte[]) && ctorParameters[i].ParameterType.FullName == SqlMapper.LinqBinary)
continue;
var unboxedType = Nullable.GetUnderlyingType(ctorParameters[i].ParameterType) ?? ctorParameters[i].ParameterType;
if (unboxedType != types[i]
&& !(unboxedType.IsEnum && Enum.GetUnderlyingType(unboxedType) == types[i])
&& !(unboxedType == typeof(char) && types[i] == typeof(string)))
break;
}

if (i == ctorParameters.Length)
return ctor;
}

return null;
}

/// <summary>
/// 查找带ExplicitConstructorAttribute特性标识的构造器
/// Returns the constructor, if any, that has the ExplicitConstructorAttribute on it.
/// </summary>
public ConstructorInfo FindExplicitConstructor()
{
var constructors = _type.GetConstructors(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
var withAttr = constructors.Where(c => c.GetCustomAttributes(typeof(ExplicitConstructorAttribute), true).Length > 0).ToList();

if (withAttr.Count == 1)
{
return withAttr[0];
}

return null;
}

/// <summary>
/// 根据构造函数和列名
/// Gets mapping for constructor parameter
/// </summary>
/// <param name="constructor">Constructor to resolve</param>
/// <param name="columnName">DataReader column name</param>
/// <returns>Mapping implementation</returns>
public SqlMapper.IMemberMap GetConstructorParameter(ConstructorInfo constructor, string columnName)
{
var parameters = constructor.GetParameters();

//注意构造器参数名与列名是相同的(忽略大小写)
return new SimpleMemberMap(columnName, parameters.FirstOrDefault(p => string.Equals(p.Name, columnName, StringComparison.OrdinalIgnoreCase)));
}

/// <summary>
/// 为某列找到映射关系,返回IMemberMap
/// Gets member mapping for column
/// </summary>
/// <param name="columnName">DataReader column name</param>
/// <returns>Mapping implementation</returns>
public SqlMapper.IMemberMap GetMember(string columnName)
{
//优先找与列名相同的属性名(优先找大小写相同的,再找不同的)。
var property = _properties.FirstOrDefault(p => string.Equals(p.Name, columnName, StringComparison.Ordinal))
?? _properties.FirstOrDefault(p => string.Equals(p.Name, columnName, StringComparison.OrdinalIgnoreCase));

//如果找不到,就尝试去掉列名下划线,再找一次。
if (property == null && MatchNamesWithUnderscores)
{
property
= _properties.FirstOrDefault(p => string.Equals(p.Name, columnName.Replace("_", ""), StringComparison.Ordinal))
?? _properties.FirstOrDefault(p => string.Equals(p.Name, columnName.Replace("_", ""), StringComparison.OrdinalIgnoreCase));
}

//如果找到就返回一个成员映射对象
if (property != null)
return new SimpleMemberMap(columnName, property);

//如果没有找到匹配的属性,就找DomainObject.Field,按照上面的套路再找一次。
var field = _fields.FirstOrDefault(p => string.Equals(p.Name, columnName, StringComparison.Ordinal))
?? _fields.FirstOrDefault(p => string.Equals(p.Name, columnName, StringComparison.OrdinalIgnoreCase));

if (field == null && MatchNamesWithUnderscores)
{
field
= _fields.FirstOrDefault(p => string.Equals(p.Name, columnName.Replace("_", ""), StringComparison.Ordinal))
?? _fields.FirstOrDefault(p => string.Equals(p.Name, columnName.Replace("_", ""), StringComparison.OrdinalIgnoreCase));
}

if (field != null)
return new SimpleMemberMap(columnName, field);

return null;
}
/// <summary>
/// 按列名匹配属性时,忽略下划线(有些时习惯在数据库中使用下划线)。
/// Should column names like User_Id be allowed to match properties/fields like UserId ?
/// </summary>
public static bool MatchNamesWithUnderscores { get; set; }
}