MongoDB request DSL • opensavvy.ktmongo.dsl.aggregation.operators • StringValueOperators • substring
substring¶
Returns the substring of a string.
The substring starts with the character at the specified Unicode code point startIndex (zero-based) in the string and continues for the length number of code points specified.
Note that this behavior is different from String.substring, which expects start and end indexes.
Counting characters¶
This function uses MongoDB's $substrCP operator, which counts characters using Unicode code points. This differs from Kotlin's String.substring, which uses UTF-16 code units. For strings containing characters outside the Basic Multilingual Plane (like emoji or certain mathematical symbols), the indexing behavior will differ.
For example, the emoji "👨👩👧👦" (family) is a single Unicode grapheme cluster but consists of multiple code points. According to this operator, it has a size of 5. However, according to Kotlin's String.substring, it has a size of 11.
Example¶
class Document(
val text: String,
)
collection.aggregate()
.set {
Document::text set of(Document::text).substring(startIndex = of(1), length = of(2))
}.toList()
External resources¶
See also¶
Returns the substring of a string.
The substring contains the Unicode code points that are contained within indexes.
Counting characters¶
This function uses MongoDB's $substrCP operator, which counts characters using Unicode code points. This differs from Kotlin's String.substring, which uses UTF-16 code units. For strings containing characters outside the Basic Multilingual Plane (like emoji or certain mathematical symbols), the indexing behavior will differ.
For example, the emoji "👨👩👧👦" (family) is a single Unicode grapheme cluster but consists of multiple code points. According to this operator, it has a size of 5. However, according to Kotlin's String.substring, it has a size of 11.
Example¶
class Document(
val text: String,
)
collection.aggregate()
.set {
Document::text set of(Document::text).substring(1..2)
}.toList()