解剖SQLSERVER 第三篇数据类型的实现（译）

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Release： 2016-06-07 15:20:01

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解剖SQLSERVER 第三篇数据类型的实现（译） http://improve.dk/implementing-data-types-in-orcamdf/ 实现对SQLSERVER数据类型的解析在OrcaMDF 软件里面是一件比较简单的事，只需要实现ISqlType 接口 public interface ISqlType{ bool IsVariableLength { g

解剖SQLSERVER 第三篇数据类型的实现（译）

http://improve.dk/implementing-data-types-in-orcamdf/

实现对SQLSERVER数据类型的解析在OrcaMDF 软件里面是一件比较简单的事，只需要实现ISqlType 接口

<span>public</span> <span>interface</span><span> ISqlType
{
    </span><span>bool</span> IsVariableLength { <span>get</span><span>; }
    </span><span>short</span>? FixedLength { <span>get</span><span>; }
    </span><span>object</span> GetValue(<span>byte</span><span>[] value);
}</span>

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IsVariableLength 返回数据类型是否是定长的还是变长的。

FixedLength 返回定长数据类型的长度，否则他返回null

数据类型解释器不关心变长字段的长度，输入的字节大小会决定长度

最后，GetValue 将输入字节参数进行解释并将字节解释为相关的.NET对象

SqlInt实现

int类型作为定长类型是非常简单的，能直接使用BitConverter进行转换

<span>public</span> <span>class</span><span> SqlInt : ISqlType
{
    </span><span>public</span> <span>bool</span><span> IsVariableLength
    {
        </span><span>get</span> { <span>return</span> <span>false</span><span>; }
    }

    </span><span>public</span> <span>short</span>?<span> FixedLength
    {
        </span><span>get</span> { <span>return</span> <span>4</span><span>; }
    }

    </span><span>public</span> <span>object</span> GetValue(<span>byte</span><span>[] value)
    {
        </span><span>if</span> (value.Length != <span>4</span><span>)
            </span><span>throw</span> <span>new</span> ArgumentException(<span>"</span><span>Invalid value length: </span><span>"</span> +<span> value.Length);

        </span><span>return</span> BitConverter.ToInt32(value, <span>0</span><span>);
    }
}</span>

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相关测试

<span>[TestFixture]
</span><span>public</span> <span>class</span><span> SqlIntTests
{
    [Test]
    </span><span>public</span> <span>void</span><span> GetValue()
    {
        </span><span>var</span> type = <span>new</span><span> SqlInt();
        </span><span>byte</span><span>[] input;

        input </span>= <span>new</span> <span>byte</span>[] { <span>0x5e</span>, <span>0x3b</span>, <span>0x27</span>, <span>0x2a</span><span> };
        Assert.AreEqual(</span><span>707214174</span><span>, Convert.ToInt32(type.GetValue(input)));

        input </span>= <span>new</span> <span>byte</span>[] { <span>0x8d</span>, <span>0xf9</span>, <span>0xaa</span>, <span>0x30</span><span> };
        Assert.AreEqual(</span><span>816511373</span><span>, Convert.ToInt32(type.GetValue(input)));

        input </span>= <span>new</span> <span>byte</span>[] { <span>0x7a</span>, <span>0x4a</span>, <span>0x72</span>, <span>0xe2</span><span> };
        Assert.AreEqual(</span>-<span>495826310</span><span>, Convert.ToInt32(type.GetValue(input)));
    }

    [Test]
    </span><span>public</span> <span>void</span><span> Length()
    {
        </span><span>var</span> type = <span>new</span><span> SqlInt();

        Assert.Throws</span><argumentexception>(() => type.GetValue(<span>new</span> <span>byte</span>[<span>3</span><span>]));
        Assert.Throws</span><argumentexception>(() => type.GetValue(<span>new</span> <span>byte</span>[<span>5</span><span>]));
    }
}</span></argumentexception></argumentexception>

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SqlNVarchar 实现

nvarchar 类型也是非常简单的，注意，如果是可变长度我们返回长度的结果是null

ISqlType 接口实现必须是无状态的

GetValue 简单的将输入的字节的数进行转换，这将转换为相关的.NET 类型，这里是string类型

<span>public</span> <span>class</span><span> SqlNVarchar : ISqlType
{
    </span><span>public</span> <span>bool</span><span> IsVariableLength
    {
        </span><span>get</span> { <span>return</span> <span>true</span><span>; }
    }

    </span><span>public</span> <span>short</span>?<span> FixedLength
    {
        </span><span>get</span> { <span>return</span> <span>null</span><span>; }
    }

    </span><span>public</span> <span>object</span> GetValue(<span>byte</span><span>[] value)
    {
        </span><span>return</span><span> Encoding.Unicode.GetString(value);
    }
}</span>

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