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Assorted fixes for jsonpath documentation 

This commit contains assorted fixes for jsonpath documentation including:
grammar fixes, incorrect examples fixes as well as wording improvements.

Discussion: https://postgr.es/m/CAA-aLv4VVX%3Db9RK5hkfPXJczqaiTdqO04teW9i0wiQVhdKcqzw%40mail.gmail.com
Author: Liudmila Mantrova
Reviewed-by: Alexander Korotkov
Reported-by: Thom Brown
This commit is contained in:
Alexander Korotkov 2019-07-10 07:46:16 +03:00
parent f7c830f1ab
commit 5a7d697a39
2 changed files with 64 additions and 53 deletions
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73
doc/src/sgml/func.sgml
View File

@ -11514,7 +11514,8 @@ table2-mapping
from the JSON data, similar to XPath expressions used
for SQL access to XML. In <productname>PostgreSQL</productname>,
path expressions are implemented as the <type>jsonpath</type>
data type, described in <xref linkend="datatype-jsonpath"/>.
data type and can use any elements described in
<xref linkend="datatype-jsonpath"/>.
</para>
<para>JSON query functions and operators
@ -11561,7 +11562,7 @@ table2-mapping
},
{ "location": [ 47.706, 13.2635 ],
"start time": "2018-10-14 10:39:21",
"HR": 130
"HR": 135
} ]
}
}
@ -11613,23 +11614,33 @@ table2-mapping
<para>
When defining the path, you can also use one or more
<firstterm>filter expressions</firstterm>, which work similar to
the <literal>WHERE</literal> clause in SQL. Each filter expression
can provide one or more filtering conditions that are applied
to the result of the path evaluation. Each filter expression must
be enclosed in parentheses and preceded by a question mark.
Filter expressions are evaluated from left to right and can be nested.
The <literal>@</literal> variable denotes the current path evaluation
result to be filtered, and can be followed by one or more accessor
operators to define the JSON element by which to filter the result.
Functions and operators that can be used in the filtering condition
are listed in <xref linkend="functions-sqljson-filter-ex-table"/>.
SQL/JSON defines three-valued logic, so the result of the filter
expression may be <literal>true</literal>, <literal>false</literal>,
<firstterm>filter expressions</firstterm> that work similar to the
<literal>WHERE</literal> clause in SQL. A filter expression begins with
a question mark and provides a condition in parentheses:
<programlisting>
? (<replaceable>condition</replaceable>)
</programlisting>
</para>
<para>
Filter expressions must be specified right after the path evaluation step
to which they are applied. The result of this step is filtered to include
only those items that satisfy the provided condition. SQL/JSON defines
three-valued logic, so the condition can be <literal>true</literal>, <literal>false</literal>,
or <literal>unknown</literal>. The <literal>unknown</literal> value
plays the same role as SQL <literal>NULL</literal>. Further path
plays the same role as SQL <literal>NULL</literal> and can be tested
for with the <literal>is unknown</literal> predicate. Further path
evaluation steps use only those items for which filter expressions
return true.
return <literal>true</literal>.
</para>
<para>
Functions and operators that can be used in filter expressions are listed
in <xref linkend="functions-sqljson-filter-ex-table"/>. The path
evaluation result to be filtered is denoted by the <literal>@</literal>
variable. To refer to a JSON element stored at a lower nesting level,
add one or more accessor operators after <literal>@</literal>.
</para>
<para>
@ -11643,8 +11654,8 @@ table2-mapping
<para>
To get the start time of segments with such values instead, you have to
filter out irrelevant segments before returning the start time, so the
filter is applied to the previous step and the path in the filtering
condition is different:
filter expression is applied to the previous step, and the path used
in the condition is different:
<programlisting>
'$.track.segments[*] ? (@.HR &gt; 130)."start time"'
</programlisting>
@ -11669,9 +11680,9 @@ table2-mapping
</para>
<para>
You can also nest filters within each other:
You can also nest filter expressions within each other:
<programlisting>
'$.track ? (@.segments[*] ? (@.HR &gt; 130)).segments.size()'
'$.track ? (exists(@.segments[*] ? (@.HR &gt; 130))).segments.size()'
</programlisting>
This expression returns the size of the track if it contains any
segments with high heart rate values, or an empty sequence otherwise.
@ -12261,7 +12272,7 @@ table2-mapping
<row>
<entry><literal>@?</literal></entry>
<entry><type>jsonpath</type></entry>
<entry>Does JSON path returns any item for the specified JSON value?</entry>
<entry>Does JSON path return any item for the specified JSON value?</entry>
<entry><literal>'{"a":[1,2,3,4,5]}'::jsonb @? '$.a[*] ? (@ > 2)'</literal></entry>
</row>
<row>
@ -12289,8 +12300,8 @@ table2-mapping
<note>
<para>
The <literal>@?</literal> and <literal>@@</literal> operators suppress
errors including: lacking object field or array element, unexpected JSON
item type and numeric errors.
the following errors: lacking object field or array element, unexpected
JSON item type, and numeric errors.
This behavior might be helpful while searching over JSON document
collections of varying structure.
</para>
@ -13146,17 +13157,17 @@ table2-mapping
<literal>jsonb_path_query</literal>, <literal>jsonb_path_query_array</literal> and
<literal>jsonb_path_query_first</literal>
functions have optional <literal>vars</literal> and <literal>silent</literal>
argument.
arguments.
</para>
<para>
When <literal>vars</literal> argument is specified, it constitutes an object
contained variables to be substituted into <literal>jsonpath</literal>
expression.
If the <literal>vars</literal> argument is specified, it provides an
object containing named variables to be substituted into a
<literal>jsonpath</literal> expression.
</para>
<para>
When <literal>silent</literal> argument is specified and has
<literal>true</literal> value, the same errors are suppressed as it is in
the <literal>@?</literal> and <literal>@@</literal> operators.
If the <literal>silent</literal> argument is specified and has the
<literal>true</literal> value, these functions suppress the same errors
as the <literal>@?</literal> and <literal>@@</literal> operators.
</para>
</note>

44
doc/src/sgml/json.sgml
View File

@ -815,21 +815,18 @@ SELECT jdoc-&gt;'guid', jdoc-&gt;'name' FROM api WHERE jdoc @&gt; '{"tags": ["qu
<literal>.**{<replaceable>level</replaceable>}</literal>
</para>
<para>
<literal>.**{<replaceable>lower_level</replaceable> to
<replaceable>upper_level</replaceable>}</literal>
</para>
<para>
<literal>.**{<replaceable>lower_level</replaceable> to
last}</literal>
<literal>.**{<replaceable>start_level</replaceable> to
<replaceable>end_level</replaceable>}</literal>
</para>
</entry>
<entry>
<para>
Same as <literal>.**</literal>, but with filter over nesting
level of JSON hierarchy. Levels are specified as integers.
Zero level corresponds to current object. This is a
<productname>PostgreSQL</productname> extension of the SQL/JSON
standard.
Same as <literal>.**</literal>, but with a filter over nesting
levels of JSON hierarchy. Nesting levels are specified as integers.
Zero level corresponds to the current object. To access the lowest
nesting level, you can use the <literal>last</literal> keyword.
This is a <productname>PostgreSQL</productname> extension of
the SQL/JSON standard.
</para>
</entry>
</row>
@ -841,19 +838,22 @@ SELECT jdoc-&gt;'guid', jdoc-&gt;'name' FROM api WHERE jdoc @&gt; '{"tags": ["qu
</entry>
<entry>
<para>
Array element accessor. <literal><replaceable>subscript</replaceable></literal>
might be given in two forms: <literal><replaceable>expr</replaceable></literal>
or <literal><replaceable>lower_expr</replaceable> to <replaceable>upper_expr</replaceable></literal>.
The first form specifies single array element by its index. The second
form specified array slice by the range of indexes. Zero index
corresponds to the first array element.
Array element accessor.
<literal><replaceable>subscript</replaceable></literal> can be
given in two forms: <literal><replaceable>index</replaceable></literal>
or <literal><replaceable>start_index</replaceable> to <replaceable>end_index</replaceable></literal>.
The first form returns a single array element by its index. The second
form returns an array slice by the range of indexes, including the
elements that correspond to the provided
<replaceable>start_index</replaceable> and <replaceable>end_index</replaceable>.
</para>
<para>
An expression in the subscript may be an integer,
numeric expression, or any other <literal>jsonpath</literal> expression
returning single numeric value. The <literal>last</literal> keyword
can be used in the expression denoting the last subscript in an array.
That's helpful for handling arrays of unknown length.
The specified <replaceable>index</replaceable> can be an integer, as
well as an expression returning a single numeric value, which is
automatically cast to integer. Zero index corresponds to the first
array element. You can also use the <literal>last</literal> keyword
to denote the last array element, which is useful for handling arrays
of unknown length.
</para>
</entry>
</row>