{"id":316437,"date":"2024-05-21T17:22:11","date_gmt":"2024-05-21T09:22:11","guid":{"rendered":"https:\/\/docs.pingcode.com\/ask\/ask-ask\/316437.html"},"modified":"2024-05-21T17:22:28","modified_gmt":"2024-05-21T09:22:28","slug":"system-dbnull-value%e4%b8%8enull%e5%8c%ba%e5%88%ab","status":"publish","type":"post","link":"https:\/\/docs.pingcode.com\/ask\/316437.html","title":{"rendered":"System.DBNull.Value\u4e0enull\u533a\u522b"},"content":{"rendered":"

\"System.DBNull.Value\u4e0enull\u533a\u522b\"<\/p>\n

DBNull.Value\u548cnull\u90fd\u7528\u4e8e\u8868\u793a\u65e0\u503c\u7684\u60c5\u51b5\uff0c\u4f46\u5b83\u4eec\u7684\u5e94\u7528\u573a\u666f\u548c\u542b\u4e49\u4e0d\u540c\u3002DBNull.Value\u662f\u4e00\u4e2a\u8868\u793a\u6570\u636e\u5e93\u4e2d\u7a7a\u503c\u7684\u5355\u4f8b\u5bf9\u8c61\uff0c\u800cnull\u7528\u4e8e\u8868\u793a\u5f15\u7528\u7c7b\u578b\u6ca1\u6709\u5f15\u7528\u4efb\u4f55\u5bf9\u8c61\u7684\u72b6\u6001<\/strong>\u3002\u5728.NET\u6846\u67b6\u4e2d\uff0cDBNull\u7528\u4e8e\u548c\u6570\u636e\u5e93\u4ea4\u4e92\uff0c\u7279\u522b\u662f\u5728\u5904\u7406\u6765\u81ea\u6570\u636e\u5e93\u7684\u7a7a\uff08NULL\uff09\u5217\u65f6\u3002\u5f53\u4ece\u6570\u636e\u5e93\u4e2d\u8bfb\u53d6\u6570\u636e\uff0c\u6216\u8005\u5411\u6570\u636e\u5e93\u4e2d\u5199\u5165\u6570\u636e\u65f6\uff0cDBNull.Value\u7528\u4e8e\u660e\u786e\u8868\u793a\u6570\u636e\u5e93\u5b57\u6bb5\u7684\u7a7a\uff08NULL\uff09\u72b6\u6001\u3002\u76f8\u5bf9\u4e8enull\uff0cDBNull.Value\u66f4\u9002\u5408\u6570\u636e\u5e93\u64cd\u4f5c\uff0c\u56e0\u4e3a\u5b83\u80fd\u591f\u88ab\u6570\u636e\u5e93\u7406\u89e3\u3002<\/p>\n<\/p>\n

\u4e00\u3001DBNULL.VALUE\u548cNULL\u7684\u5b9a\u4e49<\/h3>\n<\/p>\n

\u5728.NET\u6846\u67b6\u4e2d\uff0cDBNull\u662f\u4e00\u4e2a\u7279\u6b8a\u7684\u7c7b\uff0c\u5b83\u7684\u5b9e\u4f8bDBNull.Value\u88ab\u7528\u4e8e\u8868\u793a\u6570\u636e\u5e93\u4e2d\u7684NULL\u503c\u3002\u5f53\u6570\u636e\u5e93\u5b57\u6bb5\u4e3a\u7a7a\u65f6\uff0cADO.NET\u5728\u5c06\u6570\u636e\u4ece\u6570\u636e\u5e93\u8bfb\u5165\u7a0b\u5e8f\u65f6\u4f1a\u4f7f\u7528DBNull.Value\u6765\u4fdd\u6301\u5b57\u6bb5\u503c\u7684\u8bed\u4e49\u4e00\u81f4\u6027\u3002\u7531\u4e8e\u6570\u636e\u5e93\u4e2d\u7684NULL\u5e76\u4e0d\u7b49\u540c\u4e8e.NET\u4e2d\u7684null\uff0c\u56e0\u6b64\u9700\u8981\u8fd9\u4e2a\u7279\u6b8a\u503c\u6765\u533a\u5206\u201c\u65e0\u6570\u636e\u201d(DBNull)\u548c\u201c\u672a\u8bbe\u7f6e\u5f15\u7528\u201d(null)\u7684\u60c5\u51b5\u3002<\/p>\n<\/p>\n

\u76f8\u6bd4\u4e4b\u4e0b\uff0cnull\u5728.NET\u4e2d\u8868\u793a\u4e00\u4e2a\u5f15\u7528\u7c7b\u578b\u7684\u53d8\u91cf\u5c1a\u672a\u88ab\u521d\u59cb\u5316\uff0c\u5b83\u6ca1\u6709\u5f15\u7528\u4efb\u4f55\u5bf9\u8c61\u3002\u5f53\u4f60\u58f0\u660e\u4e00\u4e2a\u5f15\u7528\u7c7b\u578b\u53d8\u91cf\u800c\u6ca1\u6709\u7ed9\u5b83\u8d4b\u521d\u503c\u65f6\uff0c\u9ed8\u8ba4\u7684\u503c\u5c31\u662fnull\u3002\u5728.NET\u4e2d\uff0cnull\u7528\u4e8e\u6240\u6709\u7684\u5f15\u7528\u7c7b\u578b\uff0c\u6bd4\u5982\u7c7b\u3001\u63a5\u53e3\u3001\u59d4\u6258\u6216\u6570\u7ec4\u3002<\/p>\n<\/p>\n

\u4e8c\u3001\u5e94\u7528\u573a\u666f\u5dee\u5f02<\/h3>\n<\/p>\n

NULL\u7684\u4f7f\u7528\u573a\u666f<\/h4>\n<\/p>\n

null\u662f.NET\u4e2d\u5f15\u7528\u7c7b\u578b\u53d8\u91cf\u7684\u9ed8\u8ba4\u503c\uff0c\u9002\u7528\u4e8e\u4efb\u4f55\u7684\u5f15\u7528\u7c7b\u578b\uff0c\u6bd4\u5982\u7c7b\u7684\u5bf9\u8c61\u3001\u5b57\u7b26\u4e32\u3001\u6570\u7ec4\u7b49\u3002\u5f53\u4e00\u4e2a\u5f15\u7528\u7c7b\u578b\u7684\u53d8\u91cf\u88ab\u8d4b\u503c\u4e3anull\u65f6\uff0c\u610f\u5473\u7740\u5b83\u4e0d\u6307\u5411\u4efb\u4f55\u5bf9\u8c61\uff0c\u4e5f\u5c31\u662f\u8bf4\u8fd9\u4e2a\u53d8\u91cf\u662f\u7a7a\u7684\u3002\u68c0\u67e5\u4e00\u4e2a\u53d8\u91cf\u662f\u5426\u4e3anull\u662f.NET\u7a0b\u5e8f\u4e2d\u5e38\u89c1\u7684\u7a7a\u5f15\u7528\u68c0\u67e5\u64cd\u4f5c\u3002<\/p>\n<\/p>\n

DBNULL.VALUE\u7684\u4f7f\u7528\u573a\u666f<\/h4>\n<\/p>\n

DBNull.Value\u4e3b\u8981\u5e94\u7528\u4e8e\u4e0e\u6570\u636e\u5e93\u64cd\u4f5c\u76f8\u5173\u7684\u573a\u666f\u3002\u6bd4\u5982\u6267\u884c\u6570\u636e\u5e93\u67e5\u8be2\u3001\u66f4\u65b0\u3001\u63d2\u5165\u7b49\u64cd\u4f5c\u65f6\uff0c\u9700\u8981\u4e0e\u6570\u636e\u5e93\u4e2d\u7684NULL\u503c\u4e92\u76f8\u8f6c\u6362\u3002\u5728ADO.NET\u4e2dDBNull\u7528\u4e8e\u586b\u5145DataTable\u6216DataSet\u4e2d\u7684\u5217\u503c\uff0c\u4ee5\u53ca\u7528\u4e8e\u53c2\u6570\u5316\u67e5\u8be2\u4e2d\u7684\u53c2\u6570\u503c\u3002\u5b83\u544a\u8bc9\u6570\u636e\u5e93\u7cfb\u7edf\u67d0\u4e2a\u5b57\u6bb5\u662f\u7a7a\u7684\uff0c\u800c\u4e0d\u662f\u7b80\u5355\u7684\u672a\u8d4b\u503c\u72b6\u6001\u3002<\/p>\n<\/p>\n

\u4e09\u3001\u5728\u4ee3\u7801\u4e2d\u7684\u5904\u7406\u65b9\u5f0f<\/h3>\n<\/p>\n

\u5728\u5904\u7406\u6570\u636e\u5e93\u64cd\u4f5c\u65f6\uff0c\u5927\u91cf\u4f7f\u7528DBNull.Value\u53ef\u80fd\u4f1a\u8ba9\u4ee3\u7801\u53d8\u5f97\u590d\u6742\uff0c\u56e0\u4e3a\u5f00\u53d1\u8005\u5fc5\u987b\u663e\u5f0f\u5730\u68c0\u67e5\u6570\u636e\u5e93\u7684\u6bcf\u4e2a\u8fd4\u56de\u503c\u662f\u5426\u4e3aDBNull.Value\u3002\u800cnull\u7684\u68c0\u67e5\u901a\u5e38\u66f4\u7b80\u5355\uff0c\u56e0\u4e3a\u5b83\u662f\u8bed\u8a00\u5c42\u7ea7\u7684\u539f\u751f\u6982\u5ff5\uff0c\u5927\u90e8\u5206\u7684.NET\u4ee3\u7801\u90fd\u80fd\u76f4\u63a5\u5904\u7406null\u3002<\/p>\n<\/p>\n

NULL\u7684\u68c0\u67e5\u548c\u4f7f\u7528<\/h4>\n<\/p>\n

\u5728.NET\u4e2d\uff0c\u5bf9\u4e8enull\u7684\u68c0\u67e5\u975e\u5e38\u7b80\u6d01\uff1a<\/p>\n<\/p>\n

if (someObject == null)<\/p>\n
{<\/p>\n
    \/\/ \u5904\u7406\u7a7a\u5f15\u7528\u60c5\u51b5<\/p>\n
}<\/p>\n
<\/code><\/pre>\n<\/p>\n
DBNULL.VALUE\u7684\u68c0\u67e5\u548c\u4f7f\u7528<\/h4>\n<\/p>\n
\u5728.NET\u8fde\u63a5\u6570\u636e\u5e93\u65f6\uff0c\u5904\u7406DBNull.Value\u901a\u5e38\u5982\u4e0b\uff1a<\/p>\n<\/p>\n
if (dataRow["ColumnName"] == DBNull.Value)<\/p>\n
{<\/p>\n
    \/\/ \u5904\u7406\u6570\u636e\u5e93\u5217\u4e3a\u7a7a\u7684\u60c5\u51b5<\/p>\n
}<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u4e3a\u4e86\u5728\u4ee3\u7801\u4e2d\u66f4\u65b9\u4fbf\u5730\u5904\u7406DBNull\u548cnull\u7684\u8f6c\u6362\uff0c\u4e00\u4e9b\u6269\u5c55\u65b9\u6cd5\u6216\u8f85\u52a9\u7c7b\u4f1a\u88ab\u5f00\u53d1\u8005\u7528\u6765\u7b80\u5316\u8fd9\u4e00\u8fc7\u7a0b\u3002\u6bd4\u5982\uff0c\u53ef\u4ee5\u521b\u5efa\u4e00\u4e2a\u6269\u5c55\u65b9\u6cd5\u6765\u5c06DBNull\u8f6c\u6362\u4e3anull\uff0c\u6216\u8005\u53cd\u4e4b\u3002<\/p>\n<\/p>\n
\u56db\u3001\u5bf9\u7cfb\u7edf\u8bbe\u8ba1\u7684\u5f71\u54cd<\/h3>\n<\/p>\n
DBNull.Value\u548cnull\u7684\u5b58\u5728\u53cd\u6620\u4e86.NET\u6846\u67b6\u8bbe\u8ba1\u7684\u4e00\u90e8\u5206\u8003\u91cf\uff0c\u65e8\u5728\u6e05\u6670\u5730\u533a\u5206\u201c\u65e0\u6570\u636e\u201d\u548c\u201c\u672a\u8bbe\u7f6e\u201d\u8fd9\u4e24\u79cd\u573a\u666f\u3002\u5bf9\u4e8e\u6570\u636e\u5e93\u800c\u8a00\uff0c\u4e00\u4e2a\u5b57\u6bb5\u53ef\u80fd\u5b58\u5728\u4f46\u6ca1\u6709\u503c\uff08DBNull.Value\uff09\uff0c\u800c\u5bf9\u4e8e.NET\u5bf9\u8c61\u800c\u8a00\uff0cnull\u5219\u8868\u793a\u6839\u672c\u6ca1\u6709\u5bf9\u8c61\u5b9e\u4f8b\u3002<\/p>\n<\/p>\n
\u5728\u8bbe\u8ba1\u7cfb\u7edf\u548c\u6570\u636e\u5e93\u4ea4\u4e92\u65f6\uff0c\u8003\u8651DBNull\u548cnull\u7684\u533a\u5206\u5bf9\u4e8e\u907f\u514d\u9519\u8bef\u548c\u7406\u89e3\u6570\u636e\u7684\u542b\u4e49\u6781\u4e3a\u91cd\u8981\u3002\u5728\u67d0\u4e9b\u60c5\u51b5\u4e0b\uff0c\u4f8b\u5982\u5728\u6570\u636e\u5e93\u8bbe\u8ba1\u4e2d\uff0cNULL\u53ef\u80fd\u6709\u7279\u6b8a\u7684\u4e1a\u52a1\u542b\u4e49\uff0c\u800c\u5728\u5bf9\u8c61\u6a21\u578b\u8bbe\u8ba1\u4e2d\uff0cnull\u53ef\u80fd\u8868\u793a\u53ef\u5ffd\u7565\u7684\u5c5e\u6027\u6216\u672a\u521d\u59cb\u5316\u7684\u72b6\u6001\u3002<\/p>\n<\/p>\n
\u4e94\u3001\u603b\u7ed3<\/h3>\n<\/p>\n
\u603b\u7684\u6765\u8bf4\uff0cDBNull.Value\u4e0enull\u867d\u7136\u90fd\u8868\u793a\u65e0\u503c\uff0c\u4f46\u5b83\u4eec\u9002\u7528\u4e8e\u4e0d\u540c\u7684\u4e0a\u4e0b\u6587<\/strong>\u3002 DBNull.Value\u5728\u6570\u636e\u5e93\u64cd\u4f5c\u4e2d\u4f7f\u7528\uff0c\u800cnull\u5219\u662f.NET\u7f16\u7a0b\u4e2d\u5f15\u7528\u7c7b\u578b\u9ed8\u8ba4\u7684\u7a7a\u503c\u8868\u793a\u3002\u8fd9\u4e24\u8005\u7684\u533a\u522b\u5bf9\u4e8e\u7f16\u5199\u6b63\u786e\u3001\u5065\u58ef\u7684\u4ee3\u7801\u81f3\u5173\u91cd\u8981\uff0c\u5c24\u5176\u662f\u5728\u6570\u636e\u5e93\u7f16\u7a0b\u548c\u6570\u636e\u5904\u7406\u65b9\u9762\u3002\u5f00\u53d1\u8005\u5728\u7f16\u5199\u6d89\u53ca\u6570\u636e\u5e93\u548c.NET\u4e2d\u5f15\u7528\u7c7b\u578b\u7684\u4ee3\u7801\u65f6\uff0c\u9700\u8981\u6e05\u6670\u5730\u533a\u5206\u8fd9\u4e24\u4e2a\u6982\u5ff5\u4ee5\u907f\u514d\u6df7\u6dc6\u3002<\/p>\n<\/p>\n
\u76f8\u5173\u95ee\u7b54FAQs\uff1a<\/strong><\/h2>\n
1. System.DBNull.Value\u548cnull\u5728C#\u4e2d\u6709\u4ec0\u4e48\u533a\u522b\uff1f<\/strong><\/p>\n
System.DBNull.Value\u548cnull\u5728C#\u4e2d\u7528\u4e8e\u8868\u793a\u4e0d\u540c\u7684\u7a7a\u503c\u3002<\/p>\n
2. \u4e3a\u4ec0\u4e48C#\u4e2d\u9700\u8981\u4f7f\u7528System.DBNull.Value\u800c\u4e0d\u662f\u76f4\u63a5\u4f7f\u7528null\uff1f<\/strong><\/p>\n
\u5728\u6570\u636e\u8bbf\u95ee\u64cd\u4f5c\u4e2d\uff0c\u4f7f\u7528System.DBNull.Value\u53ef\u4ee5\u66f4\u51c6\u786e\u5730\u8868\u793a\u6570\u636e\u5e93\u4e2d\u7684\u7a7a\u503c\u3002\u56e0\u4e3anull\u5728C#\u4e2d\u901a\u5e38\u8868\u793a\u5f15\u7528\u7c7b\u578b\u7684\u7a7a\u503c\uff0c\u800cSystem.DBNull.Value\u7528\u4e8e\u8868\u793a\u6570\u636e\u5e93\u4e2d\u7684NULL\u503c\u3002<\/p>\n
3. \u5982\u4f55\u5c06System.DBNull.Value\u8f6c\u6362\u4e3anull\uff1f<\/strong><\/p>\n
\u4e3a\u4e86\u5c06System.DBNull.Value\u8f6c\u6362\u4e3anull\uff0c\u53ef\u4ee5\u4f7f\u7528C#\u4e2d\u7684\u6761\u4ef6\u5224\u65ad\u3002\u4f8b\u5982\uff0c\u53ef\u4ee5\u4f7f\u7528\u4e09\u5143\u8fd0\u7b97\u7b26\u5c06System.DBNull.Value\u8f6c\u6362\u4e3anull\uff0c\u793a\u4f8b\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n
object valueFromDatabase = GetColumnValueFromDatabase();\nobject convertedValue = (valueFromDatabase == System.DBNull.Value) ? null : valueFromDatabase;\n<\/code><\/pre>\n
\u901a\u8fc7\u8fd9\u79cd\u65b9\u5f0f\uff0c\u6211\u4eec\u53ef\u4ee5\u5c06\u4ece\u6570\u636e\u5e93\u4e2d\u68c0\u7d22\u7684System.DBNull.Value\u8f6c\u6362\u4e3aC#\u4e2d\u7684null\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"DBNull.Value\u548cnull\u90fd\u7528\u4e8e\u8868\u793a\u65e0\u503c\u7684\u60c5\u51b5\uff0c\u4f46\u5b83\u4eec\u7684\u5e94\u7528\u573a\u666f\u548c\u542b\u4e49\u4e0d\u540c\u3002DBNull.Value\u662f […]","protected":false},"author":3,"featured_media":316465,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[37],"tags":[],"acf":[],"_links":{"self":[{"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/posts\/316437"}],"collection":[{"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/comments?post=316437"}],"version-history":[{"count":0,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/posts\/316437\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/media\/316465"}],"wp:attachment":[{"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/media?parent=316437"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/categories?post=316437"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/tags?post=316437"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}