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Databases - Practical PostgreSQL
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Using <varparser>

LXP supports a simple search-and-replace mechanism for variable values with its <varparser> tag. This tag takes two attributes—find and replace. When you use the <varparser> tag, a region is opened within which any variable value that is substituted will be filtered through the defined search-and-replace rule.

The <varparser> is primarily useful for stripping or escaping unwanted characters. For example, in preparation to execute a SQL statement, single-quotes (') must be prefixed by a backslash, as a single-quote delimits string constants to PostgreSQL. Example 13-12 demonstrates the escaping of single-quotes in a variable called txt.

Example 13-12. Using <varparser> to prepare SQL

<lxp>
  <varparser find="'" replace="\'">
    <include sql="SELECT * FROM table WHERE txtfield = '$txt'">
      <field /><br />
    </include>
  </varparser>
</lxp>

In Example 13-12, the <varparser find="'" replace="\'"> tag instructs LXP to replace any single-quote with a back-referenced \' sequence within any substituted variable value.

Note that this search-and-replace occurs only for substituted variable values . As such, the literally typed apostrophes in the sql attribute of the <include> tag are left unchanged; only the contents of variable values being substituted within that attribute (e.g., the txt variable's value, in Example 13-12) are modified upon their substitution.

The closing </varparser> tag puts LXP back into normal variable substitution mode.

Note: You can configure several simultaneous search-and-replace rules by nesting several <varparser> tags within one another.

Databases - Practical PostgreSQL
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