package com.core.config;
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import com.baomidou.mybatisplus.annotation.DbType;
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import com.baomidou.mybatisplus.core.metadata.IPage;
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import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
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import lombok.extern.slf4j.Slf4j;
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import net.sf.jsqlparser.JSQLParserException;
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import net.sf.jsqlparser.parser.CCJSqlParserUtil;
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import net.sf.jsqlparser.statement.Statement;
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import net.sf.jsqlparser.statement.select.PlainSelect;
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import net.sf.jsqlparser.statement.select.Select;
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/**
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* Optimized pagination interceptor that avoids full-table COUNT queries
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* for pages without WHERE conditions.
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*
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* <p>Strategy:
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* <ul>
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* <li>SQL WITH WHERE clause -> delegate to parent (normal COUNT(*), indexes help)</li>
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* <li>SQL WITHOUT WHERE clause -> rewrite to simple SELECT COUNT(*) FROM table,
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* which lets InnoDB choose the smallest available index for the scan</li>
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* </ul>
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*/
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@Slf4j
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public class FastPaginationInnerInterceptor extends PaginationInnerInterceptor {
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public FastPaginationInnerInterceptor(DbType dbType) {
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super(dbType);
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}
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@Override
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public String autoCountSql(IPage<?> page, String sql) {
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if (!page.optimizeCountSql()) {
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return super.autoCountSql(page, sql);
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}
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try {
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Statement statement = CCJSqlParserUtil.parse(sql);
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if (!(statement instanceof Select)) {
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return super.autoCountSql(page, sql);
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}
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Select select = (Select) statement;
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PlainSelect plainSelect = (PlainSelect) select.getSelectBody();
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// If SQL has WHERE conditions, delegate to parent's full COUNT rewriting
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if (plainSelect.getWhere() != null) {
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return super.autoCountSql(page, sql);
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}
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// No WHERE clause — this is the "browse all records" case.
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// Return minimal COUNT query so InnoDB picks the smallest index.
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if (plainSelect.getFromItem() != null) {
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String tableName = plainSelect.getFromItem().toString();
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return "SELECT COUNT(*) FROM " + tableName;
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}
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} catch (JSQLParserException e) {
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log.debug("SQL parsing failed for fast count, using default: {}", e.getMessage());
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}
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return super.autoCountSql(page, sql);
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}
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}
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